SimpleDALRegExt (Internal Working Draft)

Status of this document

This is an IVOA Proposed Recommendation available for public review by all interested parties. Comments on this document should be made via the IVOA Request For Comment (RFC) Twiki page, http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/SimpleDALRegExt10RFC or by via email to registry at ivoa.net. The deadline comments can be found on the RFC page.

Early versions of this document were known as RegSimpleDAL. The short name is now SimpleDALRegExt.

A list of current IVOA Recommendations and other technical documents can be found at http://www.ivoa.net/Documents/.

Acknowledgements

This document has been developed with support from the National Science Foundation's Information Technology Research Program under Cooperative Agreement AST0122449 with The Johns Hopkins University, from the UK Particle Physics and Astronomy Research Council (PPARC), and from the Eurpean Commission's Sixth Framework Program via the Optical Infrared Coordination Network (OPTICON).

Conformance-related definitions

The words "MUST", "SHALL", "SHOULD", "MAY", "RECOMMENDED", and "OPTIONAL" (in upper or lower case) used in this document are to be interpreted as described in IETF standard, RFC 2119 [RFC 2119].

The Virtual Observatory (VO) is general term for a collection of federated resources that can be used to conduct astronomical research, education, and outreach. The International Virtual Observatory Alliance (IVOA) is a global collaboration of separately funded projects to develop standards and infrastructure that enable VO applications.

XML document validation is a software process that checks that an XML document is not only well-formed XML but also conforms to the syntax rules defined by the applicable schema. Typically, when the schema is defined by one or more XML Schema [schema] documents (see next section), validation refers to checking for conformance to the syntax described in those Schema documents. This document describes additional syntax constraints that cannot be enforced solely by the rules of XML Schema; thus, in this document, use of the term validation includes the extra checks that goes beyond common Schema-aware parsers which ensure conformance with this document.

Syntax Notation Using XML Schema

The eXtensible Markup Language, or XML, is document syntax for marking textual information with named tags and is defined by the World Wide Web Consortium (W3C) Recommendation, XML 1.0 [XML]. The set of XML tag names and the syntax rules for their use is referred to as the document schema. One way to formally define a schema for XML documents is using the W3C standard known as XML Schema [schema].

This document defines the VOResource schema using XML Schema. The full Schema document is listed in Appendix A. Parts of the schema appear within the main sections of this document; however, documentation nodes have been left out for the sake of brevity.

Reference to specific elements and types defined in the VOResource schema include the namespaces prefix, vr, as in vr:Resource (a type defined in the VOResource schema). Reference to specific elements and types defined in the VODataService extension schema include the namespaces prefix, vs, as in vs:ParamHTTP (a type defined in the VODataService schema). Use of the vs prefix in compliant instance documents is strongly recommended, particularly in the applications that involve IVOA Registries (see [RI], section 3.1.2). Elsewhere, the use is not required.

1. Introduction

Four data access service protocols play a key role in discovering data in the VO:

Simple Cone Search [SCS] -- searches a catalog for sources or observations that are within a given distance of a sky position.
Simple Image Access [SIA] -- searches an archive for images that overlap a given region of sky.
Simple Spectral Access [SSA] -- searches an archive for spectra of positions within a given region of sky.
Simple Line Access [SLA] -- searches a catalog specializing in descriptions of spectral line transitions.

They are called "simple" because a typical query can be formed using only a few search parameters encoded into a URL (i.e. an HTTP GET request). Their power for data discovery comes from the ability of an application to form a single query according to the rules of one of these protocols and send it to multiple services selected, say, for their relevence to a scientific topic which support that protocol. The results collected from those services, in effect then, represent all the relevent data of that type known to the VO. Thus, the key for an application wishing to do a comprehensive search of the VO is to discover all of the services that support the particular standard protocol.

Service discovery in the VO is done via a searchable registry [RI]--i.e., a searchable repository of descriptions of resources in VO. These descriptions are comprised of common standard metadata [RM] that capture information about what a resource contains or does and who provides it. A standard registry encodes these descriptions using the VOResource XML Schema [VOR]. Service resources in particular include capability metadata that describe the functionality it supports along with interface metadata that describe how to access that functionality. It is within the capability metadata that it is possible to indicate support for a particular standard protocol.

Capability metadata play an important role beyond just identifying support for a standard interface. More generally, they describe how the service behaves, and if applications are to make use of this information in an automated way, the behavior must be described using standardized metadata. In general, the metadata necessary for describing that behavior will be specific to the particular kind of service. In the case of a standard protocol, in which it is common that some variation in behavior is allowed while still being in compliance, it can be important to an application to know how a service complies with the standard for two reasons:

The application may wish to search for and select services that support a particular protocol feature. For example, an application may wish to find image services that can create cut-outs on-the-fly.

The application may wish to plan its use of the service according its limitations, such as the maximum region of sky that can be searched in one query.

It is important to note that the relevent behavioral differences between separate services that support a common protocol--and thus the metadata used to describe those behaviors--will be specific to that protocol. That is, the ability to create image cut-outs is irrelevent only to the Simple Cone Search protocol. Consequently, it is necessary to define protocol-specific metadata to adequately describe a service's support for that protocol. This document defines such capability metadata for SCS, SIA, SSA, and SLA.

This document describes, for each of the standard data access protocols--SCS, SIA, SSA, and SLA--precisely how to describe a service that supports one of the protocols in terms of the VOResource XML encoding standard [VOR]. This specification is intended to be applicable whereever VOResource records are used, but in particular, it is intended as the standard for encoding resource descriptions within an IVOA-compliant registry [RI] and for encoding capability metadata available through the VO Standard Interface [VOSI].

1.1. The Role in IVOA Architecture

The IVOA Architecture [Arch] provides a high-level view of how IVOA standards work together to connect users and applications with providers of data and services, as depicted in the diagram in Fig. 1.

Figure 1. SimpleDALRegExt in the IVOA Architecture. The Registry enables applications in the User Layer to discover archives in the Resource Layer and the services they provide for accessing data, particularly those that support the standard data access protocols like SIAP, SCS, SSAP, and SLAP (illustrated on the right). The registry metadata model standards (in blue text and boxes on the left) give structure to the information that enables that discovery. In particular, the SimpleDALRegExt standard defines the metadata used to describe standard data access services of the types listed on the right.

In this architecture, data access protocols provide the means for users (via the User Layer) to access data from archives. Of particular importance are the standard protocols, SCS, SIA, SSA, and SLA, which allow a generic user tool to find data in any archive that supports those protocols. Registries provide to tools in the User Layer a means to discover which archives support the standard protocols. A registry is a repository of descriptions of resources, such as standard services, that can be searched based on the metadata in those descriptions.

Resource descriptions have a well-defined structure: the core concepts are defined in the Resource Metadata standard [RM], and the format is defined by the VOResource XML standard [VOR]. Additional metadata specialized to describe a specific kind of service are defined via extensions to the VOResource core XML Schema. SimpleDALRegExt is one such extension specifically for describing SCS, SIA, SSA, and SLA services in the registry.

1.2. Dependencies on Other Standards

This specification relies directly on other IVOA standards in the following ways:

VOResource, v1.03 [VOR]:: Descriptions of services that support the standard protocols are encoded using the VOResource XML Schema. The protocol-specific schemas defined in this document are extensions of the VOResource core schema.
Simple Cone Search, v1.03 [SCS], Simple Image Access, v1.0 [SIA], Simple Spectral Access, v1.04 [SSA], Simple Line Access, v1.0 [SLA]:: Each protocol specification describes the metadata concepts that should be included in a description of a service that supports the specification.
VODataService, v1.1 [VDS]:: The interface to the standard protocol functionality is described with a specialized Interface type, vs:ParamHTTP, which is defined in the VODataService XML Schema, an extension to VOResource. This document also recommends describing the service using VODataService resource type, vs:CatalogDataService.

Except where noted in subsequent sections, this specification does not imply support for any other versions (including later versions) than the ones noted above.

This specification refers to other IVOA standards:

Registry Interfaces, v1.0 [RI]:: A registry that is compliant with both this specification and the Registry Interfaces standard will encode service resource descriptions according to the recommendations in this document.
IVOA Standard Interface, v1.0 [VOSI]:: A service that supports one of the target protocols as well as the capability metadata retrieval method defined by VOSI [VOSI, section 2.1] is compliant with this specifcation if the capability metadata are encoded according the recommendations in this document.

Unlike with the previously mentioned specifications, this specification may apply to later versions of the RI and VOSI standards.

2. The Common Data Model for Simple DAL Services

This section describes common requirements for describing the target DAL services as VOResource records.

To be recognized as a service, the DAL service resource must be described as a resource type of vr:Service (defined in the VOResource schema [VOR]) or one of its legal sub-types. As specified in the VOResource specification [VOR], the resource type is set by setting the xsi:type attribute on the element representing the root of the VOResource record to the namespace-qualified resource type name. As the DAL services respond to queries with tables of available data products, the resource should set the resource type to vs:CatalogService (defined in the VODataService extension schema [VDS]). In this case, record authors are encouraged to include a full description of the columns in the table returned in query response (assuming full verbosity). The vs:CatalogService resource type also allows the record to provide sky coverage information which authors are also encouraged to provide; an exception to this would be for pure SLA services as the spectral line catalogs they serve are not strictly sky observations.

Note:

In the future, a more appropriate resource type may be defined for describing DAL services; thus, the loose requirement on the resource type allows for this. At the time of this writing, the vs:CatalogService is recommended as the most appropriate type and represents current practice with IVOA registries.

The VOResource record must include a <capability> element that describes the services support for the DAL protocol. The contents of the element is described in the next section. In all cases, the value of the <capability> element's standardID unambiguously identifies the service's support for the particular DAL protocol. The resource may include other <capability> elements to describe support for other protocols.

The <capability> element describing support for the DAL protocol must include a child <interface> element that describes support for the required DAL interface; the xsi:type attribute on that element must be set to vs:ParamHTTP, and the role attribute must be set to "std". A <accessURL> element within that <interface> must be set to the base URL, as defined in the DAL protocol specification, that provides access to the standard DAL protocol. It is not necessary to provide the use attribute to the <accessURL> element (as its value can be assumed); however, when it is provided, it must be set to "base". Similarly, it is not necessary to provide the <interface> element with <queryType> or <resultType> elements; however, when provided, their values should be "GET" and "application/x-votable+xml", respectively. The vs:ParamHTTP allows one to describe input parameters supported by the service; description authors are encouraged to list the optional parameters and any custom parameters supported by the instance of the service.

A sample interface description for a simple DAL service.

 <interface xsi:type="vs:ParamHTTP" role="std">
    <accessURL use="base">
       http://adil.ncsa.uiuc.edu/cgi-bin/voimquery?survey=f&
    </accessURL>

    <!-- here is a standard, optional parameter -->
    <param use="optional" std="true">
      <name>CFRAME</name>
      <description>request to shift to a given coordinate frame.</description>
      <dataType>string</dataType>
    </param>

    <!-- here is a site-specific parameter that this service supports -->
    <param use="optional" std="false">
      <name>FREQ</name>
      <description>Frequency of observation.</description>
      <unit>Hz</unit>
      <dataType>real</dataType>
    </param>
 </interface>

3. Describing Standard Capabilities

This section describes the specific VOResource metadata extension schemas used to describe support for the target DAL protocols. The purpose of these schemas are to provide the vr:Capability sub-type that identifies the specific protocol. These are defined employing the recommendations for vr:Capability extensions given in the VOResource standard [VR]. In particular, each extension schema has the following features:

The namespace associated with the extension is a URI that is intended to resolve an HTTP URL to XML Schema document that defines the extension schema. This means that VOResource document authors may use this URI as the location URL within the value of xsi:schemaLocation attribute.

Note:

The IVOA Registry Interface standard [RI] actually requires that the VOResource records it shares with other registries provide location URLs via xsi:schemaLocation for the VOResource schema and all legal extension schemas that are used in the records. This rule would apply to the extension schemas defined in this standard.

A particular namespace prefix is recommended for use when referring to the specialized vr:Capability sub-type defined in the schema. Generally instance documents may use any prefix; however, in applications where common and consistent use of prefixes is recommended (such as with the Registry Interface specification [RI], use of the prefixes recommended in this document can be used.
The schema sets elementFormDefault="unqualified". This means that it is not necessary to qualify element names defined in the schema with a namespace prefix (as there are no global elements defined). The only place it is usually needed is as a qualifier to a Capability sub-type name given as the value of an xsi:type attribute on the <capability> element (see the examples in the subsections below).

The definition of the specialized vr:Capability sub-type fixes the value of its standardID attribute to the URI that is intended to uniquely identify the standard DAL protocol whose support the type describes.

The specialized vr:Capability sub-type includes a <testQuery> element for encoding parameters that together can be used to test the service. The format for encoding the individual parameters is customized for each of the four simple services covered in this specification.

Note:

It is also possible to encode test queries as part of the vs:ParamHTTP interface via its <testQuery> element [VDS]; this query is encoded as a single string that can be appended to the service's base URL. This specification does not recommend one over the other. Use of the vr:Capability-based <testQuery> pre-dates the vs:ParamHTTP-based one and has been kept for backward-compatibility purposes. It might be easier for some clients to use since each parameter is individually tagged and perhaps easier to parse, manipulate, and enter automatically into an interface. The vs:ParamHTTP-based one has an advantage in that it can be applied to any REST-like service, standard or not.

3.1. Simple Cone Search

This section describes the ConeSearch VOResource metadata extension schema which is used to describe services that comply with the Simple Cone Search protocol [SCS].

3.1.1. The Schema Namespace

The namespace associated with the ConeSearch extension schema is "http://www.ivoa.net/xml/ConeSearch/v1.0". The namespace prefix, cs, should be used in applications where common use of prefixes improves interoperability (e.g. in the IVOA registries [RI]). Furthermore, we use the cs prefix in this document to refer to types defined as part of the ConeSearch extension schema.

3.1.2. ConeSearch

The cs:ConeSearch type is a vr:Capability sub-type that should be used to describe a service's support for the Simple Cone Search protocol [SCS]; it is defined as follows:

cs:ConeSearch Type Schema Definition:
(Note that the purpose of type CSCapRestriction is to fix the value of standardID.)

<xs:complexType name="CSCapRestriction" abstract="true" >
  <xs:complexContent >
    <xs:restriction base="vr:Capability" >
      <xs:sequence >
        <xs:element name="validationLevel" type="vr:Validation"
                    minOccurs="0" maxOccurs="unbounded" />
        <xs:element name="description" type="xs:token" minOccurs="0" />
        <xs:element name="interface" type="vr:Interface"
                    minOccurs="0" maxOccurs="unbounded" />
      </sequence>
      <xs:attribute name="standardID" type="vr:IdentifierURI" use="required"
                    fixed="ivo://ivoa.net/std/ConeSearch" />
    </restriction>
  </complexContent>
</complexType>

<xs:complexType name="ConeSearch" >
  <xs:complexContent >
    <xs:extension base="cs:CSCapRestriction" >
      <xs:sequence >
        <xs:element name="maxSR" type="xs:float" minOccurs="0" maxOccurs="1"/>
        <xs:element name="maxRecords" type="xs:positiveInteger"
                    minOccurs="0" maxOccurs="1"/>
        <xs:element name="verbosity" type="xs:boolean" />
        <xs:element name="testQuery" type="cs:Query" minOccurs="0" maxOccurs="1"/>
      </sequence>
    </extension>
  </complexContent>
</complexType>

The cs:CSCapRestriction is defined to fix the value of the standardID attribute; thus, all uses of the cs:ConeSearch type must set standardID to "ivo://ivoa.net/std/ConeSearch". Because the cs:CSCapRestriction is marked as abstract, instance documents can not use it directly as a value for the xsi:type attribute.

The custom metadata that the cs:ConeSearch type provides is given in the table below. For the elements whose semantics map directly to service profile metadata called for in the SCS standard [SCS, section 3], there is an entry labeled "SCS Name"; this indicates the metadata name given in the SCS specification that the element in this schema corresponds to. The profile metadata listed in the SCS specification that is not covered by the elements below are covered by other metadata that are part of the core VOResource schema.

cs:ConeSearch Extension Metadata Elements
Element Definition

maxSR

SCS Name: MaxSR

Value type: floating-point number: xs:float

Semantic Meaning: The largest search radius, in degrees, that will be accepted by the service without returning an error condition. Not providing this element or specifying a value of 180 indicates that there is no restriction.

Occurrences: optional

Comments:
Not providing a value is the prefered way to indicate that there is no restriction.

maxRecords

SCS Name: MaxRecords

Value type: positive integer: xs:positiveInteger

Semantic Meaning: The largest number of records that the service will return. Not providing this value means that there is no effective limit.

Occurrences: optional

Comments:
This does not refer to the total number of records in the catalog but rather maximum number of records the service is capable of returning. A limit that is greater than the number of records available in the archive is equivalent to their being no effective limit. (See RM, Hanisch 2007.)

verbosity

SCS Name: Verbosity

Value type: boolean (true/false): xs:boolean

Semantic Meaning: True if the service supports the VERB keyword; false, otherwise.

Occurrences: required

Comments:
The value should be false if the all values of the VERB input parameter results in the same set of columns being returned.

testQuery

Value type: composite: cs:Query

Semantic Meaning: A query that will result in at least one matched record that can be used to test the service.

Occurrences: optional

3.1.2.1 testQuery and the Query Type

The <testQuery> element is intended to help other VO components (e.g. registries, validation services, services that monitor the VO's operational health--but typically not end users) test that the service is up and operating correctly. It provides a set of legal input parameters that should return a legal response that includes at least one matched record. Since this query is intended for testing purposes, the size of the result set should be small.

The cs:Query type captures the different components of the query into separate elements, as defined below:

cs:Query Type Schema Definition

<xs:complexType name="Query" >
  <xs:sequence >
    <xs:element name="ra" type="xs:double" />
    <xs:element name="dec" type="xs:double" />
    <xs:element name="sr" type="xs:double" />
    <xs:element name="verb" type="xs:positiveInteger" minOccurs="0" />
    <xs:element name="catalog" type="xs:string" minOccurs="0" />
    <xs:element name="extras" type="xs:string" minOccurs="0" />
  </sequence>
</complexType>

The individual sub-elements are defined as follows:

cs:Query Metadata Elements
Element Definition

ra

Value type: floating-point number: xs:double

Semantic Meaning: the right ascension of the search cone's center in decimal degrees.

Occurrences: required

dec

Value type: floating-point number: xs:double

Semantic Meaning: the declination of the search cone's center in decimal degrees.

Occurrences: required

sr

Value type: floating-point number: xs:double

Semantic Meaning: the radius of the search cone in decimal degrees.

Occurrences: required

verb

Value type: positive integer: xs:positiveInteger

Semantic Meaning: the verbosity level to use where 1 or less means the bare minimum set of columns and 3 or more means the full set of available columns.

Occurrences: optional

catalog

Value type: string: xs:string

Semantic Meaning: the catalog to query.

Occurrences: optional

Comments:
When the service can access more than one catalog, this input parameter, if available, is used to indicate which service to access.

extras

Value type: string: xs:string

Semantic Meaning: any extra (non-standard) parameters that must be provided (apart from what is part of base URL given by the accessURL element).

Occurrences: optional

Comments:
this value should be in the form of name=value pairs delimited with apersands (&).

3.2. Simple Image Access

This section describes the SIA VOResource metadata extension schema which is used to describe services that comply with the Simple Image Access protocol [SIA].

3.2.1. The Schema Namespace

The namespace associated with the SIA extension schema is "http://www.ivoa.net/xml/SIA/v1.1". The namespace prefix, sia, should be used in applications where common use of prefixes improves interoperability (e.g. in the IVOA registries [RI]). Furthermore, we use the sia prefix in this document to refer to types defined as part of the SIA extension schema.

3.2.2. SimpleImageAccess

The sia:SimpleImageAccess type is a vr:Capability sub-type that should be used to describe a service's support for the Simple Image Access protocol [SIA]; it is defined as follows:

sia:SimpleImageAccess Type Schema Definition
(Note that the purpose of type SIACapRestriction is to fix the value of standardID.)

<xs:complexType name="SIACapRestriction" abstract="true" >
  <xs:complexContent >
    <xs:restriction base="vr:Capability" >
      <xs:sequence >
        <xs:element name="validationLevel" type="vr:Validation"
                    minOccurs="0" maxOccurs="unbounded" />
        <xs:element name="description" type="xs:token" minOccurs="0" />
        <xs:element name="interface" type="vr:Interface"
                    minOccurs="0" maxOccurs="unbounded" />
      </sequence>
      <xs:attribute name="standardID" type="vr:IdentifierURI" use="required"
                    fixed="ivo://ivoa.net/std/SIA" />
    </restriction>
  </complexContent>
</complexType>

<xs:complexType name="SimpleImageAccess" >
  <xs:complexContent >
    <xs:extension base="sia:SIACapRestriction" >
      <xs:sequence >
        <xs:element name="imageServiceType" type="sia:ImageServiceType" />
        <xs:element name="maxQueryRegionSize" type="sia:SkySize" minOccurs="0" maxOccurs="1"/>
        <xs:element name="maxImageExtent" type="sia:SkySize" minOccurs="0" maxOccurs="1"/>
        <xs:element name="maxImageSize" type="xs:positiveInteger" minOccurs="0" maxOccurs="1"/>
        <xs:element name="maxFileSize" type="xs:positiveInteger" minOccurs="0" maxOccurs="1"/>
        <xs:element name="maxRecords" type="xs:positiveInteger" minOccurs="0" maxOccurs="1"/>
        <xs:element name="testQuery" type="sia:Query" minOccurs="0" maxOccurs="1" />
      </sequence>
    </extension>
  </complexContent>
</complexType>

The sia:SIACapRestriction is defined to fix the value of the standardID attribute; thus, all uses of the sia:SimpleImageAccess type must set standardID to "ivo://ivoa.net/std/SIA". Because the sia:SIACapRestriction is marked as abstract, instance documents can not use it directly as a value for the xsi:type attribute.

The custom metadata that the sia:SimpleImageAccess type provides is given in the table below. For the elements whose semantics map directly to metadata called for in the SIA standard [SIA, section 7], there is an entry labeled "SIA Name"; this indicates the metadata name given in the SIA specification that the element in this schema corresponds to.

sia:SimpleImageAccess Extension Metadata Elements
Element Definition

imageServiceType

SIA Name: Type.ImageService

Value type: string with controlled vocabulary

Semantic Meaning: The category of image service as defined by [SIA], section 3.

Occurrences: required

Allowed Values:

Cutout an Image Cutout Service, as defined in [SIA], section 3 (see Note below).

Mosaic an Image Mosaicing Service, as defined in [SIA], section 3 (see Note below).

Atlas an Atlas Image Archive, as defined in [SIA], section 3 (see Note below).

Pointed a Pointed Image Archive, as defined in [SIA], section 3 (see Note below).

maxQueryRegionSize

SIA Name: MaxQueryRegionSize

Value type: composite: sia:SkySize

Semantic Meaning: The maximum image query region size, expressed in decimal degrees. Not providing this element or specifying a value of 360 degrees indicates that there is no limit and the entire data collection (entire sky) can be queried.

Occurrences: optional

Comments: Not providing a value is the prefered way to indicate that there is no limit.

maxImageExtent

SIA Name: MaxImageExtent

Value type: composite: sia:SkySize

Semantic Meaning: An upper bound on a region of the sky that can be covered by returned images. That is, no image returned by this service will cover more than this limit. Not providing this element or specifying a value of 360 degrees indicates that there is no fundamental limit to the region covered by a returned image.

Occurrences: optional

Comments: When the <imageServiceType> is "Cutout" or "Mosaic", this represents the largest area that can be requested. In this case, the "no limit" value means that all-sky images can be requested. When the type is "Atlas" or "Pointed", it should be a region that most closely encloses largest images in the archive, and the "no limit" value means that the archive contains all-sky (or nearly so) images.
Not providing a value is the prefered way to indicate that there is no limit.

maxImageSize

SIA Name: MaxImageSize

Value type: positive integer: xs:positiveInteger

Semantic Meaning: A measure of the largest image the service can produce given as the maximum number of pixels along the first or second axes. Not providing a value indicates that there is no effective limit to the size of the images that can be returned.

Occurrences: optional

Comments: This is primarily relevant when the <imageServiceType> is "Cutout" or "Mosaic", indicating the largest image that can be created. When the <imageServiceType> is "Atlas" or "Pointed", this should be specified only when there are static images in the archive that can be searched for but not returned because they are too big.
When a service is more fundamentally limited by the total number of pixels in the image, this value should be set to the square-root of that number. This number will then represent a lower limit on the maximum length of a side.

maxFileSize

SIA Name: MaxFileSize

Value type: positive integer: xs:positiveInteger

Semantic Meaning: The maximum image file size in bytes. Not providing a value indicates that there is no effective limit the size of files that can be returned.

Occurrences: optional

Comments: This is primarily relevant when the <imageServiceType> is "Cutout" or "Mosaic", indicating the largest files that can be created. When the <imageServiceType> is "Atlas" or "Pointed", this should be specified only when there are static images in the archive that can be searched for but not returned because they are too big.

maxRecords

SIA Name: MaxRecords

Value type: positive integer: xs:positiveInteger

Semantic Meaning: The largest number of records that the Image Query web method will return. Not providing this value means that there is no effective limit.

Occurrences: optional

Comments: This does not refer to the total number of images in the archive but rather maximum number of records the service is capable of returning. A limit that is greater than the number of images available in the archive is equivalent to their being no effective limit. (See also [RM], Sect. 5.2.)

testQuery

Value type: composite: sia:Query

Semantic Meaning: a set of query parameters that is expected to produce at least one matched record which can be used to test the service.

Occurrences: optional

The sia:ImageServiceType type is provided to restrict the values of the <imageServiceType> element to those allowed by the SIA standard:

sia:ImageServiceType Type Schema Definition

<xs:simpleType name="ImageServiceType" >
  <xs:restriction base="xs:token" >
    <xs:enumeration value="Cutout" />
    <xs:enumeration value="Mosaic" />
    <xs:enumeration value="Atlas" />
    <xs:enumeration value="Pointed" />
  </restriction>
</simpleType>

Note:

The SIA specification defines the image service types as follows:

Image Cutout Service

This is a service which extracts or "cuts out" rectangular regions of some larger image, returning an image of the requested size to the client. Such images are usually drawn from a database or a collection of survey images that cover some large portion of the sky. To be considered a cutout service, the returned image should closely approximate (or at least not exceed) the size of the requested region; however, a cutout service will not normally resample (rescale or reproject) the pixel data. A cutout service may mosaic image segments to cover a large region but is still considered a cutout service if it does not resample the data. Image cutout services are fast and avoid image degredation due to resampling.

Image Mosaicing Service

This service is similar to the image cutout service but adds the capability to compute an image of the size, scale, and projection specified by the client. Mosaic services include services which resample and reproject existing image data, as well as services which generate pixels from some more fundamental dataset, e.g., a high energy event list or a radio astronomy measurement set. Image mosaics can be expensive to generate for large regions but they make it easier for the client to overlay image data from different sources. Image mosaicing services which resample already pixelated data will degrade the data slightly, unlike the simpler cutout service which returns the data unchanged.

Atlas Image Archive

This category of service provides access to pre-computed images that make up a survey of some large portion of the sky. The service, however, is not capable of dynamically cutting out requested regions, and the size of atlas images is predetermined by the survey. Atlas images may range in size from small cutouts of extended objects to large calibrated survey data frames.

Pointed Image Archive

This category of service provides access to collections of images of many small, "pointed" regions of the sky. "Pointed" images normally focus on specific sources in the sky as opposed to being part of a sky survey. This type of service usually applies to instrumental archives from observatories with guest observer programs (e.g., the HST archive) and other general purpose image archives (e.g., the ADIL). If a service provides access to both survey and pointed images, then it should be considered a Pointed Image Archive for the purposes of this specification; if a differentiation between the types of data is desired the pointed and survey data collections should be registered as separate image services.

Several of the sia:SimpleImageAccess metadata use complex types to capture their values; the subsequent sections below define those special types.

3.2.2.1. SkySize

The sia:SkySize type is used to capture simple rectangular extents on the sky along longitudinal and latitudinal directions. It is defined as follows:

sia:SkySize Type Schema Definition

<xs:complexType name="SkySize" >
  <xs:sequence >
    <xs:element name="long" type="xs:double" />
    <xs:element name="lat" type="xs:double" />
  </sequence>
</complexType>

The coordinate system for the region is intended to be implied by the context of its use--i.e. the definition of the element defined with this type. In this SIA case, the longitudinal and latitudinal values represent the extents along right ascension and declination in the ICRS system (the system assumed by the SIA interface).

sia:SkySize Metadata Elements
Element Definition

long

Value type: floating-point number: xs:double

Semantic Meaning: The maximum size in the longitude (R.A.) direction

Occurrences: required

lat

Value type: floating-point number: xs:double

Semantic Meaning: The maximum size in the latitude (Dec.) direction

Occurrences: required

3.2.2.3. testQuery and the Query Type

As with the other DAL vr:capability types, the <testQuery> element is intended to help other VO components (e.g. registries, validation services, services that monitor the VO's operational health--but typically not end users) test that the service is up and operating correctly. It provides a set of legal input parameters that should return a legal response that includes at least matched record. Since this query is intended for testing purposes, the size of the result set should be small.

The sia:Query type captures the different components of the query into separate elements, as defined below:

sia:Query Type Schema Definition

<xs:complexType name="Query" >
  <xs:sequence >
    <xs:element name="pos" type="sia:SkyPos" minOccurs="0" />
    <xs:element name="size" type="sia:SkySize" minOccurs="0" />
    <xs:element name="verb" type="xs:positiveInteger" minOccurs="0" />
    <xs:element name="extras" type="xs:string" minOccurs="0" />
  </sequence>
</complexType>

The individual sub-elements are defined as follows:

sia:Query Metadata Elements
Element Definition

pos

Value type: composite: sia:SkyPos

Semantic Meaning: the center position of the rectangular region that should be used as part of the query to the SIA service.

Occurrences: optional

size

Value type: composite: sia:SkySize

Semantic Meaning: the rectangular size of the region that should be used as part of the query to the SIA service.

Occurrences: optional

verb

Value type: positive integer: xs:positiveInteger

Semantic Meaning: the verbosity level to use where 1 or less means the bare minimum set of columns and 3 or more means the full set of available columns.

Occurrences: optional

extras

Value type: string: xs:string

Semantic Meaning: any extra (particularly non-standard) parameters that must be provided (apart from what is part of base URL given by the accessURL element).

Occurrences: optional

Comments:
this value should be in the form of name=value pairs delimited with apersands (&, properly escaped for inclusion into XML).

3.2.2.4. SkyPos

The sia:SkyPos type is used to encode the <testQuery>'s <pos> element, the center position of the test region of interest.

sia:SkyPos Type Schema Definition

<xs:complexType name="SkyPos" >
  <xs:sequence >
    <xs:element name="long" type="xs:double" />
    <xs:element name="lat" type="xs:double" />
  </sequence>
</complexType>

sia:SkyPos Metadata Elements
Element Definition

long

Value type: floating-point number: xs:double

Semantic Meaning: The sky position in the longitude (R.A.) direction

Occurrences: required

lat

Value type: floating-point number: xs:double

Semantic Meaning: The sky position in the latitude (Dec.) direction

Occurrences: required

3.3. Simple Spectral Access

This section describes the SSA VOResource metadata extension schema which is used to describe services that comply with the Simple Spectral Access protocol. This differs from the other Simple DAL extensions in that it defines two vr:Capability types: ssap:SimpleSpectralAccess and ssap:ProtoSpectralAccess. The former is intended for services that are intended to be compliant with published SSA Recommendation [SSA]. The latter is intended for services that were deployed prior to the publication of the SSA Recommendation (see section 3.3.3, below).

3.3.1. The Schema Namespace

The namespace associated with the SSA extension schema is "http://www.ivoa.net/xml/SSA/v1.0". The namespace prefix, ssap, should be used in applications where common use of prefixes improves interoperability (e.g. in the IVOA registries [RI]). Furthermore, we use the ssap prefix in this document to refer to types defined as part of the SSA extension schema.

Note:

Though it departs a bit from convention, the ssap prefix was chosen to avoid a collision with its use in [SSA] for identifying UTypes from the Spectral Data Model.

3.3.2. SimpleSpectralAccess

The ssap:SimpleSpectralAccess type is the vr:Capability sub-type that should be used to describe a service's support for the Simple Spectral Access protocol [SSA]; it is defined as follows:

ssap:SimpleSpectralAccess Type Schema Definition

<xs:complexType name="SSACapRestriction" abstract="true" >
  <xs:complexContent >
    <xs:restriction base="vr:Capability" >
      <xs:sequence >
        <xs:element name="validationLevel" type="vr:Validation" minOccurs="0"
            maxOccurs="unbounded" />
        <xs:element name="description" type="xs:token" minOccurs="0" />
        <xs:element name="interface" type="vr:Interface" minOccurs="0"
            maxOccurs="unbounded" />
      </sequence>
      <xs:attribute name="standardID" type="vr:IdentifierURI" use="required"
                    fixed="ivo://ivoa.net/std/SSA" />
    </restriction>
  </complexContent>
</complexType>

<xs:complexType name="SimpleSpectralAccess" >
  <xs:complexContent >
    <xs:extension base="ssap:SSACapRestriction" >
      <xs:sequence >
        <xs:element name="complianceLevel" type="ssap:ComplianceLevel" />
        <xs:element name="dataSource" type="ssap:DataSource" 
                    minOccurs="1" maxOccurs="unbounded" />
        <xs:element name="creationType" type="ssap:CreationType" 
                    minOccurs="1" maxOccurs="unbounded" />
        <xs:element name="supportedFrame" type="ssap:SupportedFrame" 
                    minOccurs="1" maxOccurs="unbounded"/>
        <xs:element name="maxSearchRadius" type="xs:double" minOccurs="0" maxOccurs="1" />
        <xs:element name="maxRecords" type="xs:positiveInteger" minOccurs="0" maxOccurs="1" />
        <xs:element name="defaultMaxRecords" type="xs:positiveInteger"
                    minOccurs="0" maxOccurs="1" />
        <xs:element name="maxAperture" type="xs:double" minOccurs="0" maxOccurs="1" />
        <xs:element name="maxFileSize" type="xs:positiveInteger" minOccurs="0" maxOccurs="1" />
        <xs:element name="testQuery" type="ssap:Query" minOccurs="0" maxOccurs="1" />
      </sequence>
    </extension>
  </complexContent>
</complexType>

The ssap:SSACapRestriction is defined to fix the value of the standardID attribute; thus, all uses of the ssap:SimpleSpectralAccess type must set standardID to "ivo://ivoa.net/std/SSA". Because the cs:SSACapRestriction is marked as abstract, instance documents can not use it directly as a value for the xsi:type attribute.

The custom metadata that the ssap:SimpleSpectralAccess type provides is given in the table below. Note that some of these elements derive from the SSA standard [SSA]; others, from the RM standard [RM]. The "Semantic Meaning" entry provides the reference to the original definition.

ssap:SimpleSpectralAccess Extension Metadata Elements
Element Definition

complianceLevel

Value type: string with controlled vocabulary

Semantic Meaning: The category indicating the level to which this instance complies with the SSA standard, as defined in [SSA], section 1.4.1.

Occurrences: required

Allowed Values:

query The service supports all of the capabilities and features of the SSA protocol identified as "must" in the specification, except that it does not support returning data in at least one SSA-compliant format.

minimal The service supports all of the capabilities and features of the SSA protocol identified as "must" in the specification.

full The service supports all of the capabilities and features of the SSA protocol identified as "must" or "should" in the specification.

dataSource

Value type: string with controlled vocabulary

Semantic Meaning: The category specifying where the data originally came from, as defined in [SSA], section 2.5.1.

Occurrences: required; multiple occurrences allowed.

Allowed Values:

survey A survey dataset, which typically covers some region of observational parameter space in a uniform fashion, with as complete as possible coverage in the region of parameter space observed.

pointed A pointed observation of a particular astronomical object or field.

custom Data which has been custom processed, e.g., as part of a specific research project.

theory Theory data, or any data generated from a theoretical model, for example a synthetic spectrum.

artificial Artificial or simulated data.

creationType

Value type: string with controlled vocabulary

Semantic Meaning: The category that describes the process used to produce the dataset, as defined in [SSA], section 2.5.1.

Occurrences: required; multiple occurrences allowed.

Allowed Values:

archival The entire archival or project dataset is returned. Transformations such as metadata or data model mediation or format conversions may take place, but the content of the dataset is not substantially modified (e.g., all the data is returned and the sample values are not modified).

cutout The dataset is subsetted in some region of parameter space to produce a subset dataset. Sample values are not modified, e.g., cutouts could be recombined to reconstitute the original dataset.

filtered The data is filtered in some fashion to exclude portions of the dataset, e.g., passing only data in selected regions along a measurement axis, or processing the data in a way which recomputes the sample values, e.g., due to interpolation or flux transformation.

mosaic Data from multiple non- or partially-overlapping datasets are combined to produce a new dataset.

projection Data is geometrically warped or dimensionally reduced by projecting through a multidimensional dataset.

specialExtraction Extraction of a spectrum from another dataset, e.g., extraction of a spectrum from a spectral data cube through a simulated aperture.

catalogExtraction Extraction of a catalog of some form from another dataset, e.g., extraction of a source catalog from an image, or extraction of a line list catalog from a spectrum (not valid for a SSA service).

Comments:
Typically this describes only the processing performed by the data service, but it could describe some additional earlier processing as well, e.g., if data is partially precomputed.

supportedFrame

Value type: string with controlled vocabulary

Semantic Meaning: The [STC] name of the space-time coordinate frames that this service can accept in. Values given here can be used as the coordinate frame argument to the SSA POS query parameter (See [SSA], secion 4.1.1.1).

Occurrences: required; multiple occurrences allowed.

Allowed Values: FK4, FK5, ECLIPTIC, ICRS, GALACTIC_I, GALACTIC_II, SUPER_GALACTIC, AZ_EL, BODY, GEO_C, GEO_D, MAG, GSE, GSM, SM, HGC, HGS, HEEQ, HRTN, HPC, HPR, HCC, HGI, MERCURY_C, VENUS_C, LUNA_C, MARS_C, JUPITER_C_III, SATURN_C_III, URANUS_C_III, NEPTUNE_C_III, PLUTO_C, MERCURY_G, VENUS_G, LUNA_G, MARS_G, JUPITER_G_III, SATURN_G_III, URANUS_G_III, NEPTUNE_G_III, PLUTO_G, UNKNOWN ; their meanings are defined in Table 3 (section 4.4.1.2.3) of [STC].

Comments: Since the [SSA] standard requires that IRCS be supported by default, the list of supported frame provided here must include at least ICRS.

maxSearchRadius

Value type: floating-point number: xs:double

Semantic Meaning: The largest search radius, in degrees, that will be accepted by the service without returning an error condition (as defined in [RM], section 5.2). Not providing this element or specifying a value of 180 indicates that there is no restriction.

Occurrences: optional

Comments:
Not providing a value is the prefered way to indicate that there is no restriction.

maxRecords

Value type: positive integer: xs:positiveInteger

Semantic Meaning: The hard limit on the largest number of records that the query operation will return in a single response (as defined in [RM], section 5.2). Not providing this value means that there is no effective limit.

Occurrences: optional

Comments: This does not refer to the total number of images in the archive but rather maximum number of records the service is capable of returning. A limit that is greater than the number of images available in the archive is equivalent to their being no effective limit. (See also [RM], Sect. 5.2.)

defaultMaxRecords

Value type:

Semantic Meaning: The largest number of records that the service will return when the MAXREC parameter not specified in the query input. Not providing a value means that the hard limit implied by <maxRecords> will be the default limit.

Occurrences: optional

maxAperture

Value type: floating-point number: xs:double

Semantic Meaning: The largest aperture that can be supported upon request via the APERTURE input parameter by a service that supports the special extraction creation method. A value of 180 or not providing a value means there is no theoretical limit.

Occurrences: optional

Comments:
Not providing a value is the preferred way to indicate that there is no limit.

maxFileSize

Value type:

Semantic Meaning: The maximum image file size in bytes.

Occurrences: optional

testQuery

Value type: composite: ssap:Query

Semantic Meaning: a set of query parameters that is expected to produce at least one matched record which can be used to test the service.

Occurrences: optional

The controlled vocabulary given for the above elements are set by their respective simple types:

ssap:ComplianceLevel Type Schema Definition

<xs:simpleType name="ComplianceLevel" >
  <xs:restriction base="xs:token" >
    <xs:enumeration value="query" />
    <xs:enumeration value="minimal" />
    <xs:enumeration value="full" />
  </restriction>
</simpleType>

ssap:DataSource Type Schema Definition

<xs:simpleType name="DataSource" >
  <xs:restriction base="xs:token" >
    <xs:enumeration value="survey" />
    <xs:enumeration value="pointed" />
    <xs:enumeration value="custom" />
    <xs:enumeration value="theory" />
    <xs:enumeration value="artificial" />
  </restriction>
</simpleType>

ssap:CreationType Type Schema Definition

<xs:simpleType name="CreationType" >
  <xs:restriction base="xs:token" >
    <xs:enumeration value="archival" />
    <xs:enumeration value="cutout" />
    <xs:enumeration value="filtered" />
    <xs:enumeration value="mosaic" />
    <xs:enumeration value="projection" />
    <xs:enumeration value="specialExtraction" />
    <xs:enumeration value="catalogExtraction" />
  </restriction>
</simpleType>

ssap:SupportedFrame Type Schema Definition

<xs:simpleType name="SupportedFrame" >
  <xs:restriction base="xs:token" >
         <xs:enumeration value="FK4"/>
         <xs:enumeration value="FK5"/>
         <xs:enumeration value="ECLIPTIC"/>
         <xs:enumeration value="ICRS"/>
         <xs:enumeration value="GALACTIC_I"/>
         <xs:enumeration value="GALACTIC_II"/>
         <xs:enumeration value="SUPER_GALACTIC"/>
         <xs:enumeration value="AZ_EL"/>
         <xs:enumeration value="BODY"/>
         <xs:enumeration value="GEO_C"/>
         <xs:enumeration value="GEO_D"/>
         <xs:enumeration value="MAG"/>
         <xs:enumeration value="GSE"/>
         <xs:enumeration value="GSM"/>
         <xs:enumeration value="HGC"/>
         <xs:enumeration value="HGS"/>
         <xs:enumeration value="HEEQ"/>
         <xs:enumeration value="HRTN"/>
         <xs:enumeration value="HPC"/>
         <xs:enumeration value="HPR"/>
         <xs:enumeration value="HCC"/>
         <xs:enumeration value="HGI"/>
         <xs:enumeration value="MERCURY_C"/>
         <xs:enumeration value="VENUS_C"/>
         <xs:enumeration value="LUNA_C"/>
         <xs:enumeration value="MARS_C"/>
         <xs:enumeration value="JUPITER_C_III"/>
         <xs:enumeration value="SATURN_C_III"/>
         <xs:enumeration value="URANUS_C_III"/>
         <xs:enumeration value="NEPTUNE_C_III"/>
         <xs:enumeration value="PLUTO_C"/>
         <xs:enumeration value="MERCURY_G"/>
         <xs:enumeration value="VENUS_G"/>
         <xs:enumeration value="LUNA_G"/>
         <xs:enumeration value="MARS_G"/>
         <xs:enumeration value="JUPITER_G_III"/>
         <xs:enumeration value="SATURN_G_III"/>
         <xs:enumeration value="URANUS_G_III"/>
         <xs:enumeration value="NEPTUNE_G_III"/>
         <xs:enumeration value="PLUTO_G"/>
         <xs:enumeration value="UNKNOWN"/>
  </restriction>
</simpleType>

The definitions of the coordinate reference frames identified in the ssap:SupportedFrame type are the same given in [STC] (and the references therein).

3.3.2.1 testQuery and the Query Type

The ssap:Query type captures the different components of the query into separate elements, as defined below:

ssap:Query Type Schema Definition

<xs:complexType name="Query" >
  <xs:sequence >
    <xs:element name="pos" type="ssap:PosParam" minOccurs="0" />
    <xs:element name="size" type="xs:double" minOccurs="0" />
    <xs:element name="queryDataCmd" type="xs:string" minOccurs="0" />
  </sequence>
</complexType>

The individual sub-elements are defined as follows:

ssap:Query Metadata Elements
Element Definition

pos

Value type: composite: ssap:PosParam

Semantic Meaning: the center position the search cone given in decimal degrees.

Occurrences: optional

size

Value type: floating-point number: xs:double

Semantic Meaning: the size of the search radius.

Occurrences: optional

queryDataCmd

Value type: string: xs:string

Semantic Meaning: Fully specified test query formatted as an URL argument list in the syntax specified by the SSA standard. The list must exclude the REQUEST argument which is assumed to be set to "queryData".

Occurrences: optional

Comments:
This value must be in the form of name=value pairs delimited with apersands (&). A query may then be formed by appending to the base URL the request argument, "REQUEST=queryData&", followed by the contents of this element.

3.3.2.2. PosParam

The ssap:PosParam type is used to encode the <testQuery>'s <pos> element, the center position of the test region of interest; it is defined as follows:

ssap:PosParam Type Schema Definition

<xs:complexType name="PosParam" >
  <xs:sequence >
    <xs:element name="long" type="xs:double" minOccurs="0" />
    <xs:element name="lat" type="xs:double" minOccurs="0" />
    <xs:element name="refframe" type="xs:token" minOccurs="0" />
  </sequence>
</complexType>

This type differs from the corresponding test position types used by the other DAL extensions in that it allows one to specify a coordinate reference frame supported by SSA's POS input parameter (see [SSA], section 4.1.1.1).

ssap:PosParam Metadata Elements
Element Definition

long

Value type: floating-point number: xs:double

Semantic Meaning: The longitude (e.g. Right Ascension) of the center of the search position in decimal degrees.

Occurrences: optional

lat

Value type: floating-point number: xs:double

Semantic Meaning: The latitude (e.g. Declination) of the center of the search position in decimal degrees.

Occurrences: optional

refframe

Value type: string: xs:token

Semantic Meaning: the coordinate system reference frame name indicating the frame to assume for the given position. If not provided, ICRS is assumed.

Occurrences: optional

3.3.3. ProtoSpectralAccess

The ssap:ProtoSpectralAccess type is provided for a special class of SSA services that were historically deployed prior to the publication of the SSA Recommendation [SSA]. An SSA service should describe its support for the protocol using this capability type if it was implemented against an earlier draft of the protocol specification and, therefore, is not expected to be compliant with the actual SSA Recommendation.

This type is defined exactly as the ssap:SimpleSpectralAccess type:

ssap:ProtoSpectralAccess Type Schema Definition

<xs:complexType name="ProtoSpectralAccess" >
  <xs:complexContent >
    <xs:extension base="ssap:SSACapRestriction" >
      <xs:sequence >
        <xs:element name="dataSource" type="ssap:DataSource" 
                    minOccurs="1" maxOccurs="unbounded" />
        <xs:element name="creationType" type="ssap:CreationType" 
                    minOccurs="1" maxOccurs="unbounded" />
        <xs:element name="supportedFrame" type="ssap:SupportedFrame" 
                    minOccurs="1" maxOccurs="unbounded"/>
        <xs:element name="maxSearchRadius" type="xs:double" minOccurs="0" maxOccurs="1" />
        <xs:element name="maxRecords" type="xs:positiveInteger" minOccurs="0" maxOccurs="1" />
        <xs:element name="defaultMaxRecords" type="xs:positiveInteger"
                    minOccurs="0" maxOccurs="1" />
        <xs:element name="maxAperture" type="xs:double" minOccurs="0" maxOccurs="1" />
        <xs:element name="maxFileSize" type="xs:positiveInteger" minOccurs="0" maxOccurs="1" />
        <xs:element name="testQuery" type="ssap:Query" minOccurs="0" maxOccurs="1" />
      </sequence>
    </extension>
  </complexContent>
</complexType>

Use of this type is intended to be temporary: providers whose SSA service falls into this category are encouraged to up-date the service for compliance with the final SSA Recommendation. A VOResource resource description must not include both a ssap:SimpleSpectralAccess capability and a ssap:ProtoSpectralAccess capability that describe the same service base URL, as given by the <interface>'s <accessURL>.

3.4. Simple Line Access

This section describes the SLA VOResource metadata extension schema which is used to describe services that comply with the Simple Line Access protocol [SLA].

3.4.1. The Schema Namespace

The namespace associated with the SLA extension schema is "http://www.ivoa.net/xml/SLAP/v1.0". The namespace prefix, slap, should be used in applications where common use of prefixes improves interoperability (e.g. in the IVOA registries [RI]). Furthermore, we use the slap prefix in this document to refer to types defined as part of the SLA extension schema.

3.4.2. SimpleLineAccess

The slap:SimpleLineAccess type is a vr:Capability sub-type that should be used to describe a service's support for the Simple Line Access protocol [SLA]; it is defined as follows:

slap:SLAPCapRestriction Type Schema Definition

<xs:complexType name="SLAPCapRestriction" abstract="true" >
  <xs:complexContent >
    <xs:restriction base="vr:Capability" >
      <xs:sequence >
        <xs:element name="validationLevel" type="vr:Validation" minOccurs="0"
                    maxOccurs="unbounded" />
        <xs:element name="description" type="xs:token" minOccurs="0" />
        <xs:element name="interface" type="vr:Interface" minOccurs="0"
                    maxOccurs="unbounded" />
      </sequence>
      <xs:attribute name="standardID" type="vr:IdentifierURI" use="required"
                    fixed="ivo://ivoa.net/std/SLAP" />
    </restriction>
  </complexContent>
</complexType>

<xs:complexType name="SimpleLineAccess" >
  <xs:complexContent >
    <xs:extension base="slap:SLAPCapRestriction" >
      <xs:sequence >
        <xs:element name="complianceLevel" type="slap:ComplianceLevel" />
        <xs:element name="dataSource" type="slap:DataSource" />
        <xs:element name="maxRecords" type="xs:positiveInteger" minOccurs="0" maxOccurs="1" />
        <xs:element name="testQuery" type="slap:Query" minOccurs="0" maxOccurs="1" />
      </sequence>
    </extension>
  </complexContent>
</complexType>

The custom metadata that the slap:SimpleLineAccess type provides is given in the table below.

slap:SimpleLineAccess Extension Metadata Elements
Element Definition

complianceLevel

Value type: string with controlled vocabulary

Semantic Meaning: The category indicating the level to which this service instance complies with the SLAP standard.

Occurrences: required

Allowed Values:

minimal The service supports all of the capabilities and features of the SLAP protocol identified as "must" in the specification.

full The service supports, at a minimum, all of the capabilities and features of the SLAP protocol identified as "must" or "should" in the specification.

Comments:
Allowed values are "minimal" and "full". See definitions of allowed values for details.

dataSource

Value type: string with controlled vocabulary

Semantic Meaning: The category specifying where the data accessed by the service originally came from.

Occurrences: required

Allowed Values:

observational/astrophysical Lines observed and identified in real spectra of astrophysical observations by different instrument/projects

observational/laboratory Lines observed and identified in real spectra of laboratory measurements

theoretical Servers containing theoretical spectral lines

Comments:
Allowed values are "observational/astrophysical", "observational/laboratory", "theoretical"

maxRecords

Value type: positive integer: xs:positiveInteger

Semantic Meaning: The hard limit on the largest number of records that the query operation will return in a single response. Not providing this value means that there is no effective limit.

Occurrences: optional

Comments:
This does not refer to the total number of records in the catalog but rather maximum number of records the service is capable of returning. A limit that is greater than the number of records available in the archive is equivalent to their being no effective limit. (See also [RM], Sect. 5.2.)

testQuery

Value type: composite: slap:Query

Semantic Meaning: A set of queryData parameters that is expected to produce at least one matched record which can be used to test the service.

Occurrences: optional

Comments:
The value should include all parameters required for the test query but should exclude the baseURL and the REQUEST parameter.

The controlled vocabulary given for the above elements are set by their respective simple types:

slap:ComplianceLevel Type Schema Definition

<xs:simpleType name="ComplianceLevel" >
  <xs:restriction base="xs:token" >
    <xs:enumeration value="minimal" />
    <xs:enumeration value="full" />
  </restriction>
</simpleType>

slap:DataSource Type Schema Definition

<xs:simpleType name="DataSource" >
  <xs:restriction base="xs:token" >
    <xs:enumeration value="observational/astrophysical" />
    <xs:enumeration value="observational/laboratory" />
    <xs:enumeration value="theoretical" />
  </restriction>
</simpleType>

3.3.2.1 testQuery and the Query Type

The slap:Query type captures the different components of the query into separate elements, as defined below:

slap:Query Type Schema Definition

<xs:complexType name="Query" >
  <xs:sequence >
    <xs:element name="wavelength" type="slap:WavelengthRange" minOccurs="0" />
    <xs:element name="queryDataCmd" type="xs:string" minOccurs="0" />
  </sequence>
</complexType>

The individual sub-elements are defined as follows:

slap:Query Metadata Elements
Element Definition

wavelength

Value type: composite: slap:WavelengthRange

Semantic Meaning: Spectral range in meters to be used to constrain the query of spectral lines.

Occurrences: optional

queryDataCmd

Value type: string: xs:string

Semantic Meaning: Fully specified queryData test query formatted as an URL argument list in the syntax specified by the SLAP standard. The list must exclude the REQUEST argument which is assumed to be set to "queryData". VERSION may be included if the test query applies to a specific version of the service protocol.

Occurrences: optional

Comments:
If queryDataCmd is used to form a query, the default value of WAVELENGTH specified above is not used; if the test query requires WAVELENGTH it should be included directly in queryDataCmd.

This value must be a string in the form of name=value pairs delimited with ampersands (&). A query may then be formed by appending to the baseURL the request argument, "REQUEST=queryData&", followed by the contents of this element.

3.4.2.2. WavelengthRange

The slap:WavelengthRange type is used to encode the <testQuery>'s <wavelength> element, the range of wavelengths to search.

slap:WavelengthRange Type Schema Definition

<xs:complexType name="WavelengthRange" >
  <xs:sequence >
    <xs:element name="minWavelength" type="xs:double" minOccurs="0" />
    <xs:element name="maxWavelength" type="xs:double" minOccurs="0" />
  </sequence>
</complexType>

slap:WavelengthRange Metadata Elements
Element Definition

minWavelength

Value type: floating-point number: xs:double

Semantic Meaning: Minimum wavelength in meters to be used to constrain the query of spectral lines

Occurrences: optional

maxWavelength

Value type: floating-point number: xs:double

Semantic Meaning: Maximum wavelength in meters to be used to constrain the query of spectral lines

Occurrences: optional

Appendix A: The XML Schemas

A.1. The ConeSearch XML Schema

The Complete ConeSearch Schema

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           xmlns:vr="http://www.ivoa.net/xml/VOResource/v1.0"
           xmlns:cs="http://www.ivoa.net/xml/ConeSearch/v1.0"
           xmlns:vm="http://www.ivoa.net/xml/VOMetadata/v0.1"
           targetNamespace="http://www.ivoa.net/xml/ConeSearch/v1.0"
           elementFormDefault="unqualified" attributeFormDefault="unqualified"
           version="1.0">

   <xs:annotation>
      <xs:appinfo>
        <vm:schemaName>ConeSearch</vm:schemaName>
        <vm:schemaPrefix>xs</vm:schemaPrefix>
        <vm:targetPrefix>cs</vm:targetPrefix>
      </xs:appinfo>
      <xs:documentation>
        Implementation of an XML Schema describing a Cone Search Service.
        Based on "Simple Cone Search: a First Guide for Data Curators",
        http://www.us-vo.org/metadata/conesearch/.
      </xs:documentation>
      <xs:documentation>
        This schema defines a Capability type that is specific to Cone
        Search.  A service that has ConeSearch capability should be 
        registered as a TabularSkyService.  The ConeSearch capability 
        element must include a ParamHTTP interface.  
      </xs:documentation>
   </xs:annotation>

   <xs:import namespace="http://www.ivoa.net/xml/VOResource/v1.0"
              schemaLocation="http://www.ivoa.net/xml/VOResource/v1.0"/>

   <xs:complexType name="CSCapRestriction" abstract="true">
      <xs:annotation>
         <xs:documentation>
            an abstract capability that fixes the standardID to the
            IVOA ID for the ConeSearch standard.
         </xs:documentation>
         <xs:documentation>
            See vr:Capability for documentation on inherited children.
         </xs:documentation>
      </xs:annotation>
      <xs:complexContent>
         <xs:restriction base="vr:Capability">
            <xs:sequence>
               <xs:element name="validationLevel" type="vr:Validation"
                           minOccurs="0" maxOccurs="unbounded"/>
               <xs:element name="description" type="xs:token" 
                           minOccurs="0"/>
               <xs:element name="interface" type="vr:Interface" 
                           minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
            <xs:attribute name="standardID" type="vr:IdentifierURI"
                          use="required" fixed="ivo://ivoa.net/std/ConeSearch"/>
         </xs:restriction>
      </xs:complexContent>
   </xs:complexType>

   <xs:complexType name="ConeSearch">
      <xs:annotation>
         <xs:documentation>
            The capabilities of a Cone Search implementation.  
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:extension base="cs:CSCapRestriction">
            <xs:sequence>
               <xs:element name="maxSR" type="xs:float"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        The largest search radius, in degrees, that will be
                        accepted by the service without returning an error 
                        condition.  Not providing this element or 
                        specifying a value of 180 indicates that there
                        is no restriction.
                     </xs:documentation>
                     <xs:documentation>
                        Not providing a value is the prefered way to indicate
                        that there is no restriction. 
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxRecords" type="xs:positiveInteger"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        The largest number of records that the service will 
                        return.  Not providing this value means that
                        there is no effective limit.  
                     </xs:documentation>
                     <xs:documentation>
                        This does not refer to the total number of records in 
                        the catalog but rather maximum number of records the 
                        service is capable of returning.  A limit that is 
                        greater than the number of records available in the 
                        archive is equivalent to their being no effective 
                        limit.  (See RM, Hanisch 2007.)
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="verbosity" type="xs:boolean">
                  <xs:annotation>
                     <xs:documentation>
                        True if the service supports the VERB keyword; 
                        false, otherwise.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="testQuery" type="cs:Query"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        A query that will result in at least on
                        matched record that can be used to test the
                        service.  
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

   <xs:complexType name="Query">
      <xs:annotation>
         <xs:documentation>
            A query to be sent to the service
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="ra" type="xs:double">
            <xs:annotation>
               <xs:documentation>
                   the right ascension of the search cone's center in
                   decimal degrees.  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="dec" type="xs:double">
            <xs:annotation>
               <xs:documentation>
                   the declination of the search cone's center in
                   decimal degrees.  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="sr" type="xs:double">
            <xs:annotation>
               <xs:documentation>
                   the radius of the search cone in decimal degrees.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="verb" type="xs:positiveInteger" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   the verbosity level to use where 1 means the bare
                   minimum set of columns and 3 means the full set of 
                   available columns.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="catalog" type="xs:string" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   the catalog to query.  
               </xs:documentation>
               <xs:documentation>
                   When the service can access more than one catalog,
                   this input parameter, if available, is used to
                   indicate which service to access.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="extras" type="xs:string" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   any extra (non-standard) parameters that must be 
                   provided (apart from what is part of base URL given 
                   by the accessURL element).
               </xs:documentation>
               <xs:documentation>
                   this value should be in the form of name=value
                   pairs delimited with ampersands (&).  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

      </xs:sequence>
   </xs:complexType>

</xs:schema>

A.2. The SIA XML Schema

The Complete SIA Schema

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           xmlns:vr="http://www.ivoa.net/xml/VOResource/v1.0"
           xmlns:sia="http://www.ivoa.net/xml/SIA/v1.1"
           xmlns:vm="http://www.ivoa.net/xml/VOMetadata/v0.1"
           targetNamespace="http://www.ivoa.net/xml/SIA/v1.1"
           elementFormDefault="unqualified" attributeFormDefault="unqualified"
           version="1.1">

   <xs:annotation>
      <xs:appinfo>
        <vm:schemaName>SIA</vm:schemaName>
        <vm:schemaPrefix>xs</vm:schemaPrefix>
        <vm:targetPrefix>sia</vm:targetPrefix>
      </xs:appinfo>
      <xs:documentation>
        Implementation of an XML Schema describing a Simple Image
        Access Service.   Based on "The Simple Image Access Specification"
        by Doug Tody et al.
      </xs:documentation>
   </xs:annotation>

   <xs:import namespace="http://www.ivoa.net/xml/VOResource/v1.0"
              schemaLocation="http://www.ivoa.net/xml/VOResource/v1.0"/>

   <xs:complexType name="SIACapRestriction" abstract="true">
      <xs:annotation>
         <xs:documentation>
            an abstract capability that fixes the standardID to the
            IVOA ID for the ConeSearch standard.
         </xs:documentation>
         <xs:documentation>
            See vr:Capability for documentation on inherited children.
         </xs:documentation>
      </xs:annotation>
      <xs:complexContent>
         <xs:restriction base="vr:Capability">
            <xs:sequence>
               <xs:element name="validationLevel" type="vr:Validation"
                           minOccurs="0" maxOccurs="unbounded"/>
               <xs:element name="description" type="xs:token" 
                           minOccurs="0"/>
               <xs:element name="interface" type="vr:Interface" 
                           minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
            <xs:attribute name="standardID" type="vr:IdentifierURI"
                          use="required" fixed="ivo://ivoa.net/std/SIA"/>
         </xs:restriction>
      </xs:complexContent>
   </xs:complexType>

   <xs:complexType name="SimpleImageAccess">
      <xs:annotation>
         <xs:documentation>
            The capabilities of an SIA implementation.  
         </xs:documentation>
         <xs:documentation>
            Editor's Notes: 
               *  This is a prototype definition to
                  illustrate how to extend the schema to a specific 
                  standard interface.
               *  Staging information is not included yet.   
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:extension base="sia:SIACapRestriction">
            <xs:sequence>
               <xs:element name="imageServiceType" type="sia:ImageServiceType">
                  <xs:annotation>
                     <xs:documentation>
                   The class of image service: Cutout, Mosaic, Atlas, Pointed
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxQueryRegionSize" type="sia:SkySize"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                         The maximum image query region size, expressed in 
                         decimal degrees.  Not providing this element or 
                         specifying a value of 360 degrees indicates that 
                         there is no limit and the entire data collection 
                         (entire sky) can be queried. 
                     </xs:documentation>
                     <xs:documentation>
                         Not providing a value is the prefered way to indicate
                         that there is no limit.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxImageExtent" type="sia:SkySize"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                         An upper bound on a region of the sky that can 
                         be covered by returned images.  That is, no image
                         returned by this service will cover more than 
                         this limit.  Not providing this element or 
                         specifying a value of 360 degrees indicates that 
                         there is no fundamental limit to the region covered 
                         by a returned image.  
                     </xs:documentation>
                     <xs:documentation>
                         When the imageServiceType is "Cutout" or "Mosaic", 
                         this represents the largest area that can be requested.
                         In this case, the "no limit" value means that all-sky
                         images can be requested.  When the type is "Atlas" or
                         "Pointed", it should be a region that most closely 
                         encloses largest images in the archive, and the "no
                         limit" value means that the archive contains all-sky 
                         (or nearly so) images.  
                     </xs:documentation>
                     <xs:documentation>
                         Not providing a value is the prefered way to indicate
                         that there is no limit.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxImageSize" type="xs:positiveInteger"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                         The largest image (in terms of pixels) that can be 
                         requested.  Not providing a value indicates that 
                         there is no effective limit to the size of the images 
                         that can be returned.  
                     </xs:documentation>
                     <xs:documentation>
                         This is primarily relevant when the imageServiceType
                         is "Cutout" or "Mosaic", indicating the largest 
                         image that can be created.  When the imageServiceType 
                         is "Atlas" or "Pointed", this should be specified only
                         when there are static images in the archive that can 
                         be searched for but not returned because they are 
                         too big.  
                     </xs:documentation>
                     <xs:documentation>
                         When a service is more fundamentally limited
                         by the total number of pixels in the image, this 
                         value should be set to the square-root of that
                         number.  This number will then represent a
                         lower limit on the maximum length of a side.  
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxFileSize" type="xs:positiveInteger"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        The maximum image file size in bytes.  Not providing 
                        a value indicates that there is no effective limit 
                        the size of files that can be returned.  
                     </xs:documentation>
                     <xs:documentation>
                        This is primarily relevant when the imageServiceType
                        is "Cutout" or "Mosaic", indicating the largest 
                        files that can be created.  When the imageServiceType 
                        is "Atlas" or "Pointed", this should be specified only
                        when there are static images in the archive that can 
                        be searched for but not returned because they are 
                        too big.  
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxRecords" type="xs:positiveInteger"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        The largest number of records that the Image Query web
                        method will return. Not providing this value means that
                        there is no effective limit.  
                     </xs:documentation>
                     <xs:documentation>
                        This does not refer to the total number of images in 
                        the archive but rather maximum number of records the 
                        service is capable of returning.  A limit that is 
                        greater than the number of images available in the 
                        archive is equivalent to their being no effective 
                        limit.  (See RM, Hanisch 2007.)
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="testQuery" type="sia:Query" 
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        a set of query parameters that is expected
                        to produce at least one matched record which
                        can be used to test the service.  
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

   <xs:complexType name="SkySize">
      <xs:sequence>
         <xs:element name="long" type="xs:double">
           <xs:annotation>
              <xs:documentation>
                 The maximum size in the longitude (R.A.) direction 
              </xs:documentation>
           </xs:annotation>
         </xs:element>
         <xs:element name="lat" type="xs:double">
           <xs:annotation>
              <xs:documentation>
                 The maximum size in the latitude (Dec.) direction 
              </xs:documentation>
           </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

   <xs:complexType name="SkyPos">
      <xs:sequence>
         <xs:element name="long" type="xs:double">
           <xs:annotation>
              <xs:documentation>
                 The sky position in the longitude (R.A.) direction 
              </xs:documentation>
           </xs:annotation>
         </xs:element>
         <xs:element name="lat" type="xs:double">
           <xs:annotation>
              <xs:documentation>
                 The sky position in the latitude (Dec.) direction 
              </xs:documentation>
           </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

   <xs:complexType name="ImageSize">
      <xs:sequence>
         <xs:element name="long" type="xs:positiveInteger">
           <xs:annotation>
              <xs:documentation>
                 The image size in the longitude (R.A.) direction in pixels
              </xs:documentation>
           </xs:annotation>
         </xs:element>
         <xs:element name="lat" type="xs:positiveInteger">
           <xs:annotation>
              <xs:documentation>
                 The image size in the latitude (Dec.) direction in pixels
              </xs:documentation>
           </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

   <xs:simpleType name="ImageServiceType">
      <xs:annotation>
         <xs:documentation>
       The class of image service: Cutout, Mosaic, Atlas, Pointed
         </xs:documentation>
      </xs:annotation>

      <xs:restriction base="xs:token">

         <xs:enumeration value="Cutout">
            <xs:annotation>
               <xs:documentation>
         This is a service which extracts or "cuts out" rectangular
         regions of some larger image, returning an image of the
         requested size to the client. Such images are usually drawn
         from a database or a collection of survey images that cover
         some large portion of the sky. To be considered a cutout
         service, the returned image should closely approximate (or at
         least not exceed) the size of the requested region; however,
         a cutout service will not normally resample (rescale or
         reproject) the pixel data. A cutout service may mosaic image
         segments to cover a large region but is still considered a
         cutout service if it does not resample the data.  Image
         cutout services are fast and avoid image degredation due to
         resampling.  
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="Mosaic">
            <xs:annotation>
               <xs:documentation>
                  This service is similar to the image cutout service
                  but adds the capability to compute an image of the
                  size, scale, and projection specified by the
                  client. Mosaic services include services which
                  resample and reproject existing image data, as well
                  as services which generate pixels from some more
                  fundamental dataset, e.g., a high energy event list
                  or a radio astronomy measurement set. Image mosaics
                  can be expensive to generate for large regions but
                  they make it easier for the client to overlay image
                  data from different sources. Image mosaicing
                  services which resample already pixelated data will
                  degrade the data slightly, unlike the simpler cutout
                  service which returns the data unchanged.  
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="Atlas">
            <xs:annotation>
               <xs:documentation>
                  This category of service provides access to
                  pre-computed images that make up a survey of some
                  large portion of the sky. The service, however, is
                  not capable of dynamically cutting out requested
                  regions, and the size of atlas images is
                  predetermined by the survey. Atlas images may range
                  in size from small cutouts of extended objects to
                  large calibrated survey data frames. 
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="Pointed">
            <xs:annotation>
               <xs:documentation>
                  This category of service provides access to
                  collections of images of many small, "pointed"
                  regions of the sky. "Pointed" images normally focus
                  on specific sources in the sky as opposed to being
                  part of a sky survey. This type of service usually
                  applies to instrumental archives from observatories
                  with guest observer programs (e.g., the HST archive)
                  and other general purpose image archives (e.g., the
                  ADIL). If a service provides access to both survey
                  and pointed images, then it should be considered a
                  Pointed Image Archive for the purposes of this
                  specification; if a differentiation between the
                  types of data is desired the pointed and survey data
                  collections should be registered as separate image
                  services.  
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

      </xs:restriction>
   </xs:simpleType>

   <xs:complexType name="Query">
      <xs:annotation>
         <xs:documentation>
            A query to be sent to the service
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="pos" type="sia:SkyPos" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   the right ascension of the search cone's center in
                   decimal degrees.  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="size" type="sia:SkySize" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   the declination of the search cone's center in
                   decimal degrees.  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="verb" type="xs:positiveInteger" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   the verbosity level to use where 0 means the bare
                   minimum set of columns and 3 means the full set of 
                   available columns.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="extras" type="xs:string" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   any extra (particularly non-standard) parameters that must 
                   be provided (apart from what is part of base URL given by 
                   the accessURL element).
               </xs:documentation>
               <xs:documentation>
                   this value should be in the form of name=value
                   pairs delimited with apersands (&).  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

      </xs:sequence>
   </xs:complexType>

</xs:schema>

A.3 The SSA XML Schema

The Complete SSA Schema

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           xmlns:vr="http://www.ivoa.net/xml/VOResource/v1.0"
           xmlns:slap="http://www.ivoa.net/xml/SLAP/v1.0"
           xmlns:vm="http://www.ivoa.net/xml/VOMetadata/v0.1"
           targetNamespace="http://www.ivoa.net/xml/SLAP/v1.0"
           elementFormDefault="unqualified" attributeFormDefault="unqualified"
           version="1.0">

   <xs:annotation>
      <xs:appinfo>
        <vm:schemaName>SLAP</vm:schemaName>
        <vm:schemaPrefix>xs</vm:schemaPrefix>
        <vm:targetPrefix>slap</vm:targetPrefix>
      </xs:appinfo>
      <xs:documentation>
        XML Schema used to describe the capabilities of a service instance
        conforming to the Simple Line Access Protocol (SLAP).
      </xs:documentation>
   </xs:annotation>

   <xs:import namespace="http://www.ivoa.net/xml/VOResource/v1.0"
              schemaLocation="http://www.ivoa.net/xml/VOResource/v1.0"/>

   <!-- Set the Capability standardID to indicate the SLAP protocol. -->
   <xs:complexType name="SLAPCapRestriction" abstract="true">
      <xs:annotation>
         <xs:documentation>
            An abstract capability that fixes the standardID to the
            IVOA ID for the SLAP standard.
         </xs:documentation>
         <xs:documentation>
            See vr:Capability for documentation on inherited children.
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:restriction base="vr:Capability">
            <xs:sequence>
               <xs:element name="validationLevel" type="vr:Validation"
                           minOccurs="0" maxOccurs="unbounded"/>
               <xs:element name="description" type="xs:token" 
                           minOccurs="0"/>
               <xs:element name="interface" type="vr:Interface" 
                           minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
            <xs:attribute name="standardID" type="vr:IdentifierURI"
                          use="required" fixed="ivo://ivoa.net/std/SLAP"/>
         </xs:restriction>
      </xs:complexContent>
   </xs:complexType>

   <!-- SLAP Capabilities -->
   <xs:complexType name="SimpleLineAccess">
      <xs:annotation>
         <xs:documentation>
            The capabilities of an SLAP service implementation.  
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:extension base="slap:SLAPCapRestriction">
            <xs:sequence>

               <xs:element name="complianceLevel" type="slap:ComplianceLevel">
                  <xs:annotation>
                     <xs:documentation>
                        The category indicating the level to which this
                        service instance complies with the SLAP standard.  
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "minimal" and "full".
                        See definitions of allowed values for details.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="dataSource" type="slap:DataSource">
                  <xs:annotation>
                     <xs:documentation>
                        The category specifying where the data accessed by
			the service originally came from. 
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "observational/astrophysical", 
			"observational/laboratory", "theoretical"
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxRecords" type="xs:positiveInteger"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        The hard limit on the largest number of records that 
                        the query operation will return in a single response.
                        Not providing this value means that there is no 
                        effective limit.  
                     </xs:documentation>
                     <xs:documentation>
                        This does not refer to the total number of spectra in 
                        the archive but rather maximum number of records the 
                        service is capable of returning.  A limit that is 
                        greater than the number of spectra available in the 
                        archive is equivalent to their being no effective 
                        limit.  (See RM, Hanisch 2007.)
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="testQuery" type="slap:Query"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        A set of queryData parameters that is expected to
			produce at least one matched record which can be
                        used to test the service.
                     </xs:documentation>
                     <xs:documentation>
		        The value should include all parameters required
			for the test query but should exclude the baseURL
			and the REQUEST parameter.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

   <xs:simpleType name="ComplianceLevel">
      <xs:annotation>
         <xs:documentation>
            The allowed values for indicating the level at which a service
	    instance complies with the SLAP standard.  
         </xs:documentation>
      </xs:annotation>

      <xs:restriction base="xs:token">
         <xs:enumeration value="minimal">
            <xs:annotation>
               <xs:documentation>
                  The service supports all of the capabilities and features
                  of the SLAP protocol identified as "must" in the 
                  specification.
               </xs:documentation>
               <xs:documentation>
                  In brief, this includes:
                    * implementing the GET interface,
                    * WAVELENGTH, REQUEST for input query,
		    * ssldm:Line.wavelength.value and ssldm:Line.title for output 
		    fields 
                    * supports the "FORMAT=METADATA" metadata query.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="full">
            <xs:annotation>
               <xs:documentation>
                  The service supports, at a minimum, all of the capabilities
		  and features of the SLAP protocol identified as "must" or
		  "should" in the specification.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>
      </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="DataSource">
      <xs:annotation>
         <xs:documentation>
           The defined categories that specify where the line data 
           originally came from, i.e., the type of data collections to
	   which the service provides access.
         </xs:documentation>
      </xs:annotation>

      <xs:restriction base="xs:token">
         <xs:enumeration value="observational/astrophysical">
            <xs:annotation>
               <xs:documentation>
                 Lines observed and identified in real spectra of
		 astrophysical observations by different
		 instrument/projects 
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="observational/laboratory">
            <xs:annotation>
               <xs:documentation>
                 Lines observed and identified in real spectra of
		 laboratory measurements
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="theoretical">
            <xs:annotation>
               <xs:documentation>
		 Servers containing theoretical spectral lines
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

      </xs:restriction>
   </xs:simpleType>

   <xs:complexType name="Query">
      <xs:annotation>
         <xs:documentation>
            A query to be sent to the service, e.g., a test query.
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="wavelength" type="slap:WavelengthRange" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  Spectral range in meters to be used to constrain the query
		  of spectral lines.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="queryDataCmd" type="xs:string" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   Fully specified queryData test query formatted as an URL
		   argument list in the syntax specified by the SLAP standard.
                   The list must exclude the REQUEST argument which is 
                   assumed to be set to "queryData".  VERSION may be
		   included if the test query applies to a specific version
		   of the service protocol.
               </xs:documentation>
               <xs:documentation>
		   If queryDataCmd is used to form a query, the default
		   value of WAVELENGTH specified above is not
		   used; if the test query requires WAVELENGTH it
		   should be included directly in queryDataCmd.
               </xs:documentation>
               <xs:documentation>
                   This value must be a string in the form of name=value
                   pairs delimited with ampersands (&).  A query may
		   then be formed by appending to the baseURL the request
		   argument, "REQUEST=queryData&", followed by the
		   contents of this element.
               </xs:documentation>
            </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

   <xs:complexType name="WavelengthRange">
      <xs:annotation>
         <xs:documentation>
            Spectral range in meters to be used to constrain the query
	    of spectral lines  
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="minWavelength" type="xs:double" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  Minimum wavelength in meters to be used to constrain the query
	    	  of spectral lines 
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="maxWavelength" type="xs:double" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  Maximum wavelength in meters to be used to constrain the query
	    	  of spectral lines
               </xs:documentation>
            </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

</xs:schema>


<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           xmlns:vr="http://www.ivoa.net/xml/VOResource/v1.0"
           xmlns:vs="http://www.ivoa.net/xml/VODataService/v1.0"
           xmlns:ssap="http://www.ivoa.net/xml/SSA/v1.0"
           xmlns:vm="http://www.ivoa.net/xml/VOMetadata/v0.1"
           targetNamespace="http://www.ivoa.net/xml/SSA/v1.0"
           elementFormDefault="unqualified" attributeFormDefault="unqualified"
           version="1.0">

   <xs:annotation>
      <xs:appinfo>
        <vm:schemaName>SSA</vm:schemaName>
        <vm:schemaPrefix>xs</vm:schemaPrefix>
        <vm:targetPrefix>ssap</vm:targetPrefix>
      </xs:appinfo>
      <xs:documentation>
        XML Schema used to describe the capabilities of a service instance
        conforming to the Simple Spectral Access (SSA) protocol.
      </xs:documentation>
   </xs:annotation>

   <xs:import namespace="http://www.ivoa.net/xml/VOResource/v1.0"
              schemaLocation="http://www.ivoa.net/xml/VOResource/v1.0"/>
   <xs:import namespace="http://www.ivoa.net/xml/VODataService/v1.0"
              schemaLocation="http://www.ivoa.net/xml/VODataService/v1.0"/>

   <!-- Set the Capability standardID to indicate the SSA protocol. -->
   <xs:complexType name="SSACapRestriction" abstract="true">
      <xs:annotation>
         <xs:documentation>
            An abstract capability that fixes the standardID to the
            IVOA ID for the SSA standard.
         </xs:documentation>
         <xs:documentation>
            See vr:Capability for documentation on inherited children.
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:restriction base="vr:Capability">
            <xs:sequence>
               <xs:element name="validationLevel" type="vr:Validation"
                           minOccurs="0" maxOccurs="unbounded"/>
               <xs:element name="description" type="xs:token" 
                           minOccurs="0"/>
               <xs:element name="interface" type="vr:Interface" 
                           minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
            <xs:attribute name="standardID" type="vr:IdentifierURI"
                          use="required" fixed="ivo://ivoa.net/std/SSA"/>
         </xs:restriction>
      </xs:complexContent>
   </xs:complexType>

   <!-- SSA Capabilities -->
   <xs:complexType name="SimpleSpectralAccess">
      <xs:annotation>
         <xs:documentation>
            The capabilities of an SSA service implementation.  
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:extension base="ssap:SSACapRestriction">
            <xs:sequence>

               <xs:element name="complianceLevel" type="ssap:ComplianceLevel">
                  <xs:annotation>
                     <xs:documentation>
                        The category indicating the level to which
                        this instance complies with the SSA standard.  
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "query", "minimal", and "full".
                        See definitions of allowed values for details.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="dataSource" type="ssap:DataSource"
                           minOccurs="1" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:documentation>
                        The category specifying where the data originally 
                        came from. 
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "survey", "pointed", "custom",
                        "theory", "artificial"
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="creationType" type="ssap:CreationType"
                           minOccurs="1" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:documentation>
                        The category that describes the process used to 
                        produce the dataset.  
                     </xs:documentation>
                     <xs:documentation>
                        Typically this describes only the processing 
                        performed by the data service, but it could 
                        describe some additional earlier processing as 
                        well, e.g., if data is partially precomputed. 
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "archival", "cutout", "filtered",
                        "mosaic", "projection", "spectralExtraction", 
                        "catalogExtraction"
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="supportedFrame" type="ssap:SupportedFrame"
                           minOccurs="1" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:documentation>
                        The STC name for a world coordinate system 
                        frame supported by this service.
                     </xs:documentation>
                     <xs:documentation>
                        At least one recognized value must be listed.
                        With SSA v1.1, ICRS must be supported; thus,
                        this list must include at least this value.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxSearchRadius" type="xs:double">
                  <xs:annotation>
                     <xs:documentation>
                        The largest search radius, in degrees, that will be
                        accepted by the service without returning an error 
                        condition.
                     </xs:documentation>
                     <xs:documentation>
                        Use 180.0 if there is no restriction.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxRecords" type="xs:int">
                  <xs:annotation>
                     <xs:documentation>
                        The hard limit on the largest number of records that 
                        the query operation will return in a single response
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="defaultMaxRecords" type="xs:int">
                  <xs:annotation>
                     <xs:documentation>
                        The largest number of records that the service will
                        return when the MAXREC parameter not specified
                        in the query input.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxAperture" type="xs:double"
                           minOccurs="0">
                  <xs:annotation>
                     <xs:documentation>
                        The largest aperture that can be supported upon 
                        request via the APERTURE input parameter by a 
                        service that supports the special extraction 
                        creation method.  
                     </xs:documentation>
                     <xs:documentation>
                        A value of 180 (the default) means there is no 
                        theoretical limit.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxFileSize" type="xs:int"
                           maxOccurs="1" minOccurs="0">
                  <xs:annotation>
                     <xs:documentation>
                        The maximum image file size in bytes.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="testQuery" type="ssap:Query"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        a set of query parameters that is expected to
                        produce at least one matched record which can be
                        used to test the service.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

   <xs:simpleType name="ComplianceLevel">
      <xs:annotation>
         <xs:documentation>
            The allowed values for indicating the level at which a 
            service instance complies with the SSA standard.  
         </xs:documentation>
      </xs:annotation>

      <xs:restriction base="xs:token">
         <xs:enumeration value="query">
            <xs:annotation>
               <xs:documentation>
                  The service supports all of the capabilities and features
                  of the SSA protocol identified as "must" in the 
                  specification, except that it does not support returning 
                  data in at least one SSA-compliant format.
               </xs:documentation>
               <xs:documentation>
                  This level represents the lowest level of compliance.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="minimal">
            <xs:annotation>
               <xs:documentation>
                  The service supports all of the capabilities and features
                  of the SSA protocol identified as "must" in the 
                  specification.
               </xs:documentation>
               <xs:documentation>
                  In brief, this includes:
                    *  implementing the GET interface,
                    *  support the parameters POS, SIZE, TOME, BAND, and 
                         FORMAT
                    *  includes all mandatory metadata fields in query 
                         response
                    *  supports getData method retrieval in at least one 
                         SSA-compliant format
                    *  supports the "FORMAT=METADATA" metadata query.
               </xs:documentation>
               <xs:documentation>
                  This level represents the middle level of compliance.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="full">
            <xs:annotation>
               <xs:documentation>
                  The service supports all of the capabilities and features
                  of the SSA protocol identified as "must" or "should" in the 
                  specification.
               </xs:documentation>
               <xs:documentation>
                  This level represents the highest level of compliance.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>
      </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="DataSource">
      <xs:annotation>
         <xs:documentation>
           The defined categories that specify where the spectral data 
           originally came from. 
         </xs:documentation>
      </xs:annotation>

      <xs:restriction base="xs:token">
         <xs:enumeration value="survey">
            <xs:annotation>
               <xs:documentation>
                  A survey dataset, which typically covers some region of 
                  observational parameter space in a uniform fashion, with 
                  as complete as possible coverage in the region of parameter 
                  space observed.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="pointed">
            <xs:annotation>
               <xs:documentation>
                  A pointed observation of a particular astronomical object 
                  or field. 
               </xs:documentation>
               <xs:documentation>
                  Typically, these are instrumental observations taken as 
                  part of some PI observing program. The data quality and 
                  characteristics may be variable, but the observations of 
                  a particular object or field may be more extensive than 
                  for a survey.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="custom">
            <xs:annotation>
               <xs:documentation>
                  Data which has been custom processed, e.g., as part of 
                  a specific research project.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="theory">
            <xs:annotation>
               <xs:documentation>
                  Theory data, or any data generated from a theoretical 
                  model, for example a synthetic spectrum.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="artificial">
            <xs:annotation>
               <xs:documentation>
                  Artificial or simulated data. 
               </xs:documentation>
               <xs:documentation>
                  This is similar to theory data but need not be based on 
                  a physical model, and is often used for testing purposes.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

      </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="CreationType">
      <xs:restriction base="xs:token">
         <xs:enumeration value="archival">
            <xs:annotation>
               <xs:documentation>
                  The entire archival or project dataset is returned.
                  Transformations such as metadata or data model mediation
                  or format conversions may take place, but the content of 
                  the dataset is not substantially modified (e.g., all the 
                  data is returned and the sample values are not modified).
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="cutout">
            <xs:annotation>
               <xs:documentation>
                  The dataset is subsetted in some region of parameter 
                  space to produce a subset dataset. Sample values are not 
                  modified, e.g., cutouts could be recombined to reconstitute 
                  the original dataset.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="filtered">
            <xs:annotation>
               <xs:documentation>
                  The data is filtered in some fashion to exclude portions 
                  of the dataset, e.g., passing only data in selected regions 
                  along a measurement axis, or processing the data in a way 
                  which recomputes the sample values, e.g., due to 
                  interpolation or flux transformation. 
               </xs:documentation>
               <xs:documentation>
                  Filtering is often 
                  combined with other forms of processing, e.g., projection.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="mosaic">
            <xs:annotation>
               <xs:documentation>
                  Data from multiple non- or partially-overlapping datasets 
                  are combined to produce a new dataset.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="projection">
            <xs:annotation>
               <xs:documentation>
                  Data is geometrically warped or dimensionally reduced by
                  projecting through a multidimensional dataset.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="specialExtraction">
            <xs:annotation>
               <xs:documentation>
                  Extraction of a spectrum from another dataset, e.g.,
                  extraction of a spectrum from a spectral data cube 
                  through a simulated aperture.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="catalogExtraction">
            <xs:annotation>
               <xs:documentation>
                  Extraction of a catalog of some form from another dataset,
                  e.g., extraction of a source catalog from an image, or
                  extraction of a line list catalog from a spectrum (not 
                  valid for a SSA service).
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

      </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="SupportedFrame">
      <xs:annotation>
        <xs:documentation>
          A controlled list of space-time reference frame names
          defined from Table 3 (S 4.4.1.2.3) of the STC spec.  
        </xs:documentation>
      </xs:annotation>

      <xs:restriction base="xs:token">
         <xs:enumeration value="FK4">
            <xs:annotation>
               <xs:documentation>
                  the Fundemental Katalog, system 4, frame; Besselian
               </xs:documentation>
               <xs:documentation>
                  Spectrum data files will require a specification of
                  the equinox; if it is not expressed explicitly,
                  B1950.0 should be assumed.  
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="FK5">
            <xs:annotation>
               <xs:documentation>
                  the Fundemental Katalog, system 5, frame; Julien
               </xs:documentation>
               <xs:documentation>
                  Spectrum data files will require a specification of
                  the equinox; if it is not expressed explicitly,
                  J2000.0 should be assumed.  
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="ECLIPTIC">
            <xs:annotation>
               <xs:documentation>
                  Ecliptic coordinates
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="ICRS">
            <xs:annotation>
               <xs:documentation>
                  International Celestial Reference System
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="GALACTIC_I">
            <xs:annotation>
               <xs:documentation>
                  old Galactic coordinates
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="GALACTIC_II">
            <xs:annotation>
               <xs:documentation>
                  old Galactic coordinates
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="SUPER_GALACTIC">
            <xs:annotation>
               <xs:documentation>
                  Super-galactic coordinates with the north pole at
                  GALACTIC_II (47.37, +6.32) and the origin at 
                  GALACTIC_II (137.37, 0).
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="AZ_EL">
            <xs:annotation>
               <xs:documentation>
                  The local azimuth and elevation frame where azimuth 
                  increases from north through east.  
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="BODY">
            <xs:annotation>
               <xs:documentation>
                  A generic solar system body-centered coordinate frame
               </xs:documentation>
               <xs:documentation>
                  If applicable, queries against this system should assume a 
                  default magnitude value or range in the absence of an 
                  applicable (non-standard) query constraint.  Service 
                  providers are encouraged to document the such assumptions 
                  in the resource or capability description.   
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="GEO_C">
            <xs:annotation>
               <xs:documentation>
                  3D Geographic (geocentric) coordinates where the magnitude
                  is expressed as a geocentric distance
               </xs:documentation>
               <xs:documentation>
                  If applicable, queries against this system should assume a 
                  default magnitude value or range in the absence of an 
                  applicable (non-standard) query constraint.  Service 
                  providers are encouraged to document the such assumptions 
                  in the resource or capability description.   
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="GEO_D">
            <xs:annotation>
               <xs:documentation>
                  3D Geographic (geocentric) coordinates where the magnitude
                  is expressed as an elevation above sea-level.  
               </xs:documentation>
               <xs:documentation>
                  If applicable, queries against this system should assume a 
                  default magnitude value or range in the absence of an 
                  applicable (non-standard) query constraint.  Service 
                  providers are encouraged to document the such assumptions 
                  in the resource or capability description.   
               </xs:documentation>
               <xs:documentation>
                  Semi-major axis and inverse flattening of the
                  reference spheroid may need to be assumed; a 
                  default as defined by the IAU 1976 is recommended.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="MAG">
            <xs:annotation>
               <xs:documentation>
                  Geomagnetic coordinates.  
               </xs:documentation>
               <xs:documentation>
                  See Franz and Harper 2002, Planetary and Space
                  Science, vol 50, p. 217.
               </xs:documentation>
               <xs:documentation>
                  If applicable, queries against this system should assume a 
                  default magnitude value or range in the absence of an 
                  applicable (non-standard) query constraint.  Service 
                  providers are encouraged to document the such assumptions 
                  in the resource or capability description.   
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="GSE">
            <xs:annotation>
               <xs:documentation>
                  Geocentric Solar Ecliptic coordinates
               </xs:documentation>
               <xs:documentation>
                  See Franz and Harper 2002, Planetary and Space
                  Science, vol 50, p. 217.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="GSM">
            <xs:annotation>
               <xs:documentation>
                  Geocentric Solar Magnetic coordinates
               </xs:documentation>
               <xs:documentation>
                  See Franz and Harper 2002, Planetary and Space
                  Science, vol 50, p. 217.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="HGC">
            <xs:annotation>
               <xs:documentation>
                  Heliographic coordinates (Carrington)
               </xs:documentation>
               <xs:documentation>
                  See Thompson 2006, "Coordinate Systems for Solar
                  Image Data", A&A., Section 2.2
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="HGS">
            <xs:annotation>
               <xs:documentation>
                  Heliographic coordinates (Stonyhurst)
               </xs:documentation>
               <xs:documentation>
                  See Thompson 2006, "Coordinate Systems for Solar
                  Image Data", A&A., Section 2.2
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="HEEQ">
            <xs:annotation>
               <xs:documentation>
                  Heliographic Earth Equatorial coordinates
               </xs:documentation>
               <xs:documentation>
                  See Franz and Harper 2002, Planetary and Space
                  Science, vol 50, p. 217, and 
                  Thompson 2006, "Coordinate Systems for Solar
                  Image Data", A&A., Section 2.1
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="HRTN">
            <xs:annotation>
               <xs:documentation>
                  Heliographic Radial-Tangential-Normal coordinates
               </xs:documentation>
               <xs:documentation>
                  See Franz and Harper 2002, Planetary and Space
                  Science, vol 50, p. 217.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="HPC">
            <xs:annotation>
               <xs:documentation>
                  Helioprojective Cartesian coordinates
               </xs:documentation>
               <xs:documentation>
                  See Thompson 2006, "Coordinate Systems for Solar
                  Image Data", A&A., Section 2.1
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="HPR">
            <xs:annotation>
               <xs:documentation>
                  Helioprojective Polar coordinates
               </xs:documentation>
               <xs:documentation>
                  See Thompson 2006, "Coordinate Systems for Solar
                  Image Data", A&A., Section 2.1
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="HCC">
            <xs:annotation>
               <xs:documentation>
                  Heliocentric Cartesian coordinates
               </xs:documentation>
               <xs:documentation>
                  See Thompson 2006, "Coordinate Systems for Solar
                  Image Data", A&A., Section 2.1
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="HGI">
            <xs:annotation>
               <xs:documentation>
                  Heliographic Inertial coordinates
               </xs:documentation>
               <xs:documentation>
                  See Franz and Harper 2002, Planetary and Space
                  Science, vol 50, p. 217.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="MERCURY_C">
            <xs:annotation>
               <xs:documentation>
                  Planteocentric coordinates on Mercury
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="VENUS_C">
            <xs:annotation>
               <xs:documentation>
                  Planteocentric coordinates on Venus
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="LUNA_C">
            <xs:annotation>
               <xs:documentation>
                  Selenocentric coordinates (for the Moon)
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="MARS_C">
            <xs:annotation>
               <xs:documentation>
                  Planteocentric coordinates on Mars
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="JUPITER_C_III">
            <xs:annotation>
               <xs:documentation>
                  Planteocentric coordinates on Jupiter, system III
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="SATURN_C_III">
            <xs:annotation>
               <xs:documentation>
                  Planteocentric coordinates on Saturn, system III
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="URANUS_C_III">
            <xs:annotation>
               <xs:documentation>
                  Planteocentric coordinates on Uranus, system III
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="NEPTUNE_C_III">
            <xs:annotation>
               <xs:documentation>
                  Planteocentric coordinates on Neptune, system III
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="PLUTO_C">
            <xs:annotation>
               <xs:documentation>
                  Planteocentric coordinates on Mercury
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="MERCURY_G">
            <xs:annotation>
               <xs:documentation>
                  Planteographic coordinates on Mercury
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="VENUS_G">
            <xs:annotation>
               <xs:documentation>
                  Planteographic coordinates on Venus
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="LUNA_G">
            <xs:annotation>
               <xs:documentation>
                  Selenographic coordinates (for the Moon)
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="MARS_G">
            <xs:annotation>
               <xs:documentation>
                  Planteographic coordinates on Mars
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="JUPITER_G_III">
            <xs:annotation>
               <xs:documentation>
                  Planteographic coordinates on Jupiter, system III
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="SATURN_G_III">
            <xs:annotation>
               <xs:documentation>
                  Planteographic coordinates on Saturn, system III
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="URANUS_G_III">
            <xs:annotation>
               <xs:documentation>
                  Planteographic coordinates on Uranus, system III
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="NEPTUNE_G_III">
            <xs:annotation>
               <xs:documentation>
                  Planteographic coordinates on Neptune, system III
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="PLUTO_G">
            <xs:annotation>
               <xs:documentation>
                  Planteographic coordinates on Mercury
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="UNKNOWN">
            <xs:annotation>
               <xs:documentation>
                  a frame that is either unknown or non-standard
               </xs:documentation>
               <xs:documentation>
                  Any available descriptive details should be
                  given (or referenced) in the capability's description.  
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

      </xs:restriction>
   </xs:simpleType>

   <xs:complexType name="Query">
      <xs:annotation>
         <xs:documentation>
            A query to be sent to the service
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="pos" type="ssap:PosParam" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   the center position the search cone given in
                   decimal degrees.  
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="size" type="xs:double" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  the size of the search radius.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="queryDataCmd" type="xs:string" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   Fully specified test query formatted as an URL
                   argument list in the syntax specified by the SSA standard.
                   The list must exclude the REQUEST argument which is 
                   assumed to be set to "queryData".
               </xs:documentation>
               <xs:documentation>
                   This value must be in the form of name=value
                   pairs delimited with apersands (&).  A query
                   may then be formed by appending to the base URL the
                   request argument, "REQUEST=queryData&", followed
                   by the contents of this element.
               </xs:documentation>
            </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

   <xs:complexType name="PosParam">
      <xs:annotation>
         <xs:documentation>
            a position in the sky to search.
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="long" type="xs:double" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  The longitude (e.g. Right Ascension) of the center of the
                  search position in decimal degrees.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="lat" type="xs:double" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  The latitude (e.g. Declination) of the center of the
                  search position in decimal degrees.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="refframe" type="xs:token" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  the coordinate system reference frame name indicating
                  the frame to assume for the given position.   If not 
                  provided, ICRS is assumed.
               </xs:documentation>
            </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

   <!--
     -  a separate type for pre-v1.0 compliant spectral services.  
     --> 
   <xs:complexType name="ProtoSpectralAccess">
      <xs:annotation>
         <xs:documentation>
            The capabilities of an proto-SSA service implementation.
            Clients may assume a particular interface for this type of
            service based on historical convention; however, no
            guarantees are made that the service is compliant with any 
            IVOA standard.  
         </xs:documentation>
         <xs:documentation>
            This capability is for spectral access services developed
            prior to the completion of the SSA standard and,
            therefore, are not compliant with that standard.
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:extension base="ssap:SSACapRestriction">
            <xs:sequence>

               <xs:element name="dataSource" type="ssap:DataSource"
                           minOccurs="1" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:documentation>
                        The category specifying where the data originally 
                        came from. 
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "survey", "pointed", "custom",
                        "theory", "artificial"
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="creationType" type="ssap:CreationType"
                           minOccurs="1" maxOccurs="unbounded">
                  <xs:annotation>
                     <xs:documentation>
                        The category that describes the process used to 
                        produce the dataset.  
                     </xs:documentation>
                     <xs:documentation>
                        Typically this describes only the processing 
                        performed by the data service, but it could 
                        describe some additional earlier processing as 
                        well, e.g., if data is partially precomputed. 
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "archival", "cutout", "filtered",
                        "mosaic", "projection", "spectralExtraction", 
                        "catalogExtraction"
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxSearchRadius" type="xs:double">
                  <xs:annotation>
                     <xs:documentation>
                        The largest search radius, in degrees, that will be
                        accepted by the service without returning an error 
                        condition.
                     </xs:documentation>
                     <xs:documentation>
                        Use 180.0 if there is no restriction.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxRecords" type="xs:int">
                  <xs:annotation>
                     <xs:documentation>
                        The hard limit on the largest number of records that 
                        the query operation will return in a single response
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="defaultMaxRecords" type="xs:int">
                  <xs:annotation>
                     <xs:documentation>
                        The largest number of records that the service will
                        return when the MAXREC parameter not specified
                        in the query input.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxAperture" type="xs:double"
                           minOccurs="0">
                  <xs:annotation>
                     <xs:documentation>
                        The largest aperture that can be supported upon 
                        request via the APERTURE input parameter by a 
                        service that supports the special extraction 
                        creation method.  
                     </xs:documentation>
                     <xs:documentation>
                        A value of 180 (the default) means there is no 
                        theoretical limit.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxFileSize" type="xs:int"
                           maxOccurs="1" minOccurs="0">
                  <xs:annotation>
                     <xs:documentation>
                        The maximum image file size in bytes.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="testQuery" type="ssap:Query"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        a set of query parameters that is expected to
                        produce at least one matched record which can be
                        used to test the service.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

</xs:schema>

A.4. The SLAP XML Schema

The Complete SLA Schema

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           xmlns:vr="http://www.ivoa.net/xml/VOResource/v1.0"
           xmlns:slap="http://www.ivoa.net/xml/SLAP/v1.0"
           xmlns:vm="http://www.ivoa.net/xml/VOMetadata/v0.1"
           targetNamespace="http://www.ivoa.net/xml/SLAP/v1.0"
           elementFormDefault="unqualified" attributeFormDefault="unqualified"
           version="1.0">

   <xs:annotation>
      <xs:appinfo>
        <vm:schemaName>SLAP</vm:schemaName>
        <vm:schemaPrefix>xs</vm:schemaPrefix>
        <vm:targetPrefix>slap</vm:targetPrefix>
      </xs:appinfo>
      <xs:documentation>
        XML Schema used to describe the capabilities of a service instance
        conforming to the Simple Line Access Protocol (SLAP).
      </xs:documentation>
   </xs:annotation>

   <xs:import namespace="http://www.ivoa.net/xml/VOResource/v1.0"
              schemaLocation="http://www.ivoa.net/xml/VOResource/v1.0"/>

   <!-- Set the Capability standardID to indicate the SLAP protocol. -->
   <xs:complexType name="SLAPCapRestriction" abstract="true">
      <xs:annotation>
         <xs:documentation>
            An abstract capability that fixes the standardID to the
            IVOA ID for the SLAP standard.
         </xs:documentation>
         <xs:documentation>
            See vr:Capability for documentation on inherited children.
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:restriction base="vr:Capability">
            <xs:sequence>
               <xs:element name="validationLevel" type="vr:Validation"
                           minOccurs="0" maxOccurs="unbounded"/>
               <xs:element name="description" type="xs:token" 
                           minOccurs="0"/>
               <xs:element name="interface" type="vr:Interface" 
                           minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
            <xs:attribute name="standardID" type="vr:IdentifierURI"
                          use="required" fixed="ivo://ivoa.net/std/SLAP"/>
         </xs:restriction>
      </xs:complexContent>
   </xs:complexType>

   <!-- SLAP Capabilities -->
   <xs:complexType name="SimpleLineAccess">
      <xs:annotation>
         <xs:documentation>
            The capabilities of an SLAP service implementation.  
         </xs:documentation>
      </xs:annotation>

      <xs:complexContent>
         <xs:extension base="slap:SLAPCapRestriction">
            <xs:sequence>

               <xs:element name="complianceLevel" type="slap:ComplianceLevel">
                  <xs:annotation>
                     <xs:documentation>
                        The category indicating the level to which this
                        service instance complies with the SLAP standard.  
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "minimal" and "full".
                        See definitions of allowed values for details.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="dataSource" type="slap:DataSource">
                  <xs:annotation>
                     <xs:documentation>
                        The category specifying where the data accessed by
			the service originally came from. 
                     </xs:documentation>
                     <xs:documentation>
                        Allowed values are "observational/astrophysical", 
			"observational/laboratory", "theoretical"
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="maxRecords" type="xs:positiveInteger"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        The hard limit on the largest number of records that 
                        the query operation will return in a single response.
                        Not providing this value means that there is no 
                        effective limit.  
                     </xs:documentation>
                     <xs:documentation>
                        This does not refer to the total number of spectra in 
                        the archive but rather maximum number of records the 
                        service is capable of returning.  A limit that is 
                        greater than the number of spectra available in the 
                        archive is equivalent to their being no effective 
                        limit.  (See RM, Hanisch 2007.)
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

               <xs:element name="testQuery" type="slap:Query"
                           minOccurs="0" maxOccurs="1">
                  <xs:annotation>
                     <xs:documentation>
                        A set of queryData parameters that is expected to
			produce at least one matched record which can be
                        used to test the service.
                     </xs:documentation>
                     <xs:documentation>
		        The value should include all parameters required
			for the test query but should exclude the baseURL
			and the REQUEST parameter.
                     </xs:documentation>
                  </xs:annotation>
               </xs:element>

            </xs:sequence>
         </xs:extension>
      </xs:complexContent>
   </xs:complexType>

   <xs:simpleType name="ComplianceLevel">
      <xs:annotation>
         <xs:documentation>
            The allowed values for indicating the level at which a service
	    instance complies with the SLAP standard.  
         </xs:documentation>
      </xs:annotation>

      <xs:restriction base="xs:token">
         <xs:enumeration value="minimal">
            <xs:annotation>
               <xs:documentation>
                  The service supports all of the capabilities and features
                  of the SLAP protocol identified as "must" in the 
                  specification.
               </xs:documentation>
               <xs:documentation>
                  In brief, this includes:
                    * implementing the GET interface,
                    * WAVELENGTH, REQUEST for input query,
		    * ssldm:Line.wavelength.value and ssldm:Line.title for output 
		    fields 
                    * supports the "FORMAT=METADATA" metadata query.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="full">
            <xs:annotation>
               <xs:documentation>
                  The service supports, at a minimum, all of the capabilities
		  and features of the SLAP protocol identified as "must" or
		  "should" in the specification.
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>
      </xs:restriction>
   </xs:simpleType>

   <xs:simpleType name="DataSource">
      <xs:annotation>
         <xs:documentation>
           The defined categories that specify where the line data 
           originally came from, i.e., the type of data collections to
	   which the service provides access.
         </xs:documentation>
      </xs:annotation>

      <xs:restriction base="xs:token">
         <xs:enumeration value="observational/astrophysical">
            <xs:annotation>
               <xs:documentation>
                 Lines observed and identified in real spectra of
		 astrophysical observations by different
		 instrument/projects 
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="observational/laboratory">
            <xs:annotation>
               <xs:documentation>
                 Lines observed and identified in real spectra of
		 laboratory measurements
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

         <xs:enumeration value="theoretical">
            <xs:annotation>
               <xs:documentation>
		 Servers containing theoretical spectral lines
               </xs:documentation>
            </xs:annotation>
         </xs:enumeration>

      </xs:restriction>
   </xs:simpleType>

   <xs:complexType name="Query">
      <xs:annotation>
         <xs:documentation>
            A query to be sent to the service, e.g., a test query.
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="wavelength" type="slap:WavelengthRange" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  Spectral range in meters to be used to constrain the query
		  of spectral lines.
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="queryDataCmd" type="xs:string" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                   Fully specified queryData test query formatted as an URL
		   argument list in the syntax specified by the SLAP standard.
                   The list must exclude the REQUEST argument which is 
                   assumed to be set to "queryData".  VERSION may be
		   included if the test query applies to a specific version
		   of the service protocol.
               </xs:documentation>
               <xs:documentation>
		   If queryDataCmd is used to form a query, the default
		   value of WAVELENGTH specified above is not
		   used; if the test query requires WAVELENGTH it
		   should be included directly in queryDataCmd.
               </xs:documentation>
               <xs:documentation>
                   This value must be a string in the form of name=value
                   pairs delimited with ampersands (&).  A query may
		   then be formed by appending to the baseURL the request
		   argument, "REQUEST=queryData&", followed by the
		   contents of this element.
               </xs:documentation>
            </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

   <xs:complexType name="WavelengthRange">
      <xs:annotation>
         <xs:documentation>
            Spectral range in meters to be used to constrain the query
	    of spectral lines  
         </xs:documentation>
      </xs:annotation>

      <xs:sequence>
         <xs:element name="minWavelength" type="xs:double" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  Minimum wavelength in meters to be used to constrain the query
	    	  of spectral lines 
               </xs:documentation>
            </xs:annotation>
         </xs:element>

         <xs:element name="maxWavelength" type="xs:double" minOccurs="0">
            <xs:annotation>
               <xs:documentation>
                  Maximum wavelength in meters to be used to constrain the query
	    	  of spectral lines
               </xs:documentation>
            </xs:annotation>
         </xs:element>
      </xs:sequence>
   </xs:complexType>

</xs:schema>

Appendix B: Supporting Multiple Versions of DAL Protocols

Note: this section is non-normative.

It is possible for a VOResource-encoded resource description to indicate support for multiple versions of standard service. This is described generally in Section 2.2.2 ("The Service Data Model") of the VOResource specification [VOR]. In that section, the specification says that a <capability> element can contain multiple <interface> elements, each describing a different version. In this appendix, we illustrate how this can be applied to the DAL services covered by this (SimpleDALRegExt) specification.

We start by noting that the standardID values for each of the DAL protocols described in this document refer to the standards generally, without reference to the particular version. For example, the IVOA identifier for the Simple Cone Search protocol is ivo://ivoa.net/std/ConeSearch. Thus a <capability> element can logically describe support for any version or multiple versions of the standard DAL protocol as long as the extension schema for that protocol is same for all of the versions.

Here is an example a service that supports two versions of the SSA protocol:

Example

Supporting multiple versions of the SSA standard. Below shows just the <capability> element of a description of an SSA service resource.

  <capability xsi:type="ssap:SimpleSpectralAccess" standardID="ivo://ivoa.net/std/SSA">

     <description>
       This service supports the SSA protocol standard.  Currently, there is 
       support for both 1.04 and 1.1 versions of the spec.  A browser-based
       front-end is also available.  
     </description>

     <!--
       -  this gives the base URL for the standard GET interface, version 1.1
       -->
     <interface xsi:type="vs:ParamHTTP" role="std" version="1.1">
        <accessURL use="base">
           http://adil.ncsa.uiuc.edu/cgi-bin/vossa11
        </accessURL>
     </interface>

     <!--
       -  this gives the base URL for the standard GET interface, version 1.04
       -->
     <interface xsi:type="vs:ParamHTTP" role="std" version="1.04">
        <accessURL use="base">
           http://adil.ncsa.uiuc.edu/cgi-bin/vossa
        </accessURL>
     </interface>

     <!--
       -  Here's an interactive version.  Since it's just a front-end to 
       -  the GET service, it shares the same capability metadata.
       -  This element does not have a version attribute nor is role="std"
       -  set, since it is not part of the standard.
       -->
     <interface xsi:type="vr:WebBrowser">
        <accessURL> http://adil.ncsa.uiuc.edu/ws/vossa </accessURL>
     </interface>

     <!--
       -  This starts the SSA-specific metadata
       -->
     <complianceLevel>full</complianceLevel>
     <dataSource>pointed</dataSource>
     <creationType>cutout</creationType>
     <maxSearchRadius>10</maxSearchRadius>
     <maxRecords>10000</maxRecords>
     <defaultMaxRecords>500</defaultMaxRecords>
     <maxAperture>3600</maxAperture>

  </capability>

In the above example, two different SSA service endpoints are supported, each compliant with a different version of the SSA standard. The version attribute on the <interface> elements indicate which version the endpoint supports. Note that if a version attribute is not provided, it defaults to "1.0". The role="std" distinguishes standard-complying interfaces from custom ones; in the example above, an endpoint to a browser-based front-end is provided as well.

A consumer that wishes to engage a standard DAL service, should extract interface descriptions where role="std" is set. From of those, the consumer should inspect the version attribute to select a version that it supports.

Often, the difference between versions is of little consequence to a consumer, so having to choose between several standardized versions is an unneeded complication. Thus, it is recommended that publishers list the most preferred version for users (typically the latest) first among the list of interfaces; consequently, consumers that do not care to attempt to interpret the version attribute should choose the first in the list. If the service query fails (because the consumer's assumptions about the service protocol are not applicable to that version of the service), the consumer may try the next one in the list.

Appendix C: Change History

Changes from PR-v1.0 20120517

The namespace URIs given in Sections 3.1.1, 3.2.1, 3.3.1, and 3.4.1 were updated to match that specified in the XSDs (i.e. to include a "v" preceding the version field).
Several capability metadata with types xs:int and xs:float were changed to xs:positiveInterger xs:double to allow for larger/more precise numbers.
Capability metadata that indicated maximum allowed values (e.g. <maxRecords>, <maxImageSize>, etc.) were made optional to avoid large, meaningless numbers from being provided. Now not specifying a value is the preferred way to indicate that no upper limit applies.
Semantic definition of <sia:maxImageExtent> clarified to differentiate it from <sia:maxQueryRegionSize>
The type for <sia:maxImageSize> was changed to xs:positiveInteger, a single number that represents the length of a side in pixels. The sia:ImageSize type (no longer needed) was dropped.
The version field in the SIA namespace was incremented to 1.1 due to the non-backward-compatible change to <sia:maxImageSize>
various typos and grammatical errors corrected.

Changes from WD-v1.0 20110921:

Now recommend ssap as prefix; changed all occurances of ssa in text and schema.
added <supportedFrame> to ssap:SimpleSpectralAccess
removed import of VODataService schema from SIA, SSA, and Conesearch schemas.
change base type of controlled vocab types from xs:string to xs:token for consistancy with VOResource.

References

[RFC 2119]: Bradner, S. 1997. Key words for use in RFCs to Indicate Requirement Levels, IETF RFC 2119, http://www.ietf.org/rfc/rfc2119.txt
[schema]: Fallside, David C., Walmsley, Priscilla (editors) 2004, XML Schema Part 0: Primer Second Edition, W3C Recommendation 28 October 2004, http://www.w3.org/TR/xmlschema-0/
[Arch]: Arviset, Christophe and the IVOA Tehcnical Coordination Group 2010, The IVOA in 2010: Technical Assessment and Roadmap, v1.0, IVOA Note, in preparation.
[SCS]: Williams, R., Hanisch, R., Szalay, A., and Plante, R. 2008, Simple Cone Search Version 1.03, IVOA Recommendation, 22 February 2008, http://www.ivoa.net/Documents/REC/DAL/ConeSearch-20080222.html.
[SIA]: Tody, D. and Plante, R. 2004, Simple Image Access Specification Version 1.0, IVOA Working Draft, http://www.ivoa.net/Documents/WD/SIA/sia-20040524.html.
[SSA]: Tody, D., Dolensky, M., McDowell, J., Bonnarel, F., Budavari, T., Busko, I., Micol, A., Osuna, P, Salgado, J., Skoda, P., Thompson, R., and Valdes, F. 2008, Simple Spectral Access Protocol Version 1.04, IVOA Recommendation, 01 Febrary 2008, http://www.ivoa.net/Documents/cover/SSA-20080201.html.
[SLA]: Salgado, J., Osuna, P., Guainazzi, M., Barbarisi, I., Dubernet, M., and Tody. D. 2010, Simple Line Access Protocol Version 1.0, IVOA Recommendation, 9 December 2010, http://www.ivoa.net/Documents/SLAP/20101209/.
[RI]: Benson, Kevin, Plante, Ray, Auden, Elizabeth, Graham, Matthew, Greene, Gretchen, Hill, Martin, Linde, Tony, Morris, Dave, O'Mullane, Wil, Rixon, Guy, Andrews, Kona 2008, IVOA Registry Interfaces, v1.02, IVOA Recommendation, http://www.ivoa.net/Documents/latest/ResourceInterface.html
[RM]: Hanisch, Robert (ed.) 2004. Resource Metadata for the Virtual Observatory, Version 1.12, IVOA Recommendation, http://www.ivoa.net/Documents/REC/ResMetadata/RM-20040426.htm
[VOR]: Plante, R., Benson, K., Graham, M., Greene, G., Harrison, P., Lemson, G., Linde, T., Rixon, G., Stébé, A. 2008, VOResource: an XML Encoding Schema for Resource Metadata, v1.03, IVOA Recommendation, http://www.ivoa.net/Documents/REC/ReR/VOResource-20080222.html
[VDS]: Plante, R., Stébé, A. Benson, K., Dowler, P. Graham, M., Greene, G., Harrison, P., Lemson, G., Linde, T., Rixon, G., Stébé, A. 2009, VODataService: a VOResource Schema Extension for Describing Collections and Services, v1.1, IVOA Recommendation, http://www.ivoa.net/Documents/VODataService/20101202/
[STC]: Rots, Arnold 2007, Space-Time Coordinate Metadata for the Virtual Observatory, v1.33, IVOA Recommendation, href="http://www.ivoa.net/Documents/REC/STC/STC-20071030.html">

Describing Simple Data Access Services Version 1.0

IVOA Proposed Recommendation 16 November 2012

Conformance-related definitions

Syntax Notation Using XML Schema

1.1. The Role in IVOA Architecture

1.2. Dependencies on Other Standards

2. The Common Data Model for Simple DAL Services

3. Describing Standard Capabilities

3.1. Simple Cone Search

3.1.1. The Schema Namespace

3.1.2. ConeSearch

3.1.2.1 testQuery and the Query Type

3.2. Simple Image Access

3.2.1. The Schema Namespace

3.2.2. SimpleImageAccess

3.2.2.1. SkySize

3.2.2.3. testQuery and the Query Type

3.2.2.4. SkyPos

3.3. Simple Spectral Access

3.3.1. The Schema Namespace

3.3.2. SimpleSpectralAccess

3.3.2.1 testQuery and the Query Type

3.3.2.2. PosParam

3.3.3. ProtoSpectralAccess

3.4. Simple Line Access

3.4.1. The Schema Namespace

3.4.2. SimpleLineAccess

3.3.2.1 testQuery and the Query Type

3.4.2.2. WavelengthRange

Appendix A: The XML Schemas

Appendix B: Supporting Multiple Versions of DAL Protocols

Appendix C: Change History

Changes from PR-v1.0 20120517

Changes from WD-v1.0 20110921:

Describing Simple Data Access Services
Version 1.0