Describing SSA services as a VO resource

Part of the standardization of a protocol is defining an XML schema for describing an instance of the service, primarily in a VO registry. This is done by creating an extension of the VOResource schema.

Working Draft Schemas

Two working draft versions are currently available.

SSA-wd.xsd: This is the version for Working Group discussion.
an example

Note

this version is under final internal review; barring further comments, it will be released as an external working draft schema.

Recent changes:

• add clone of SimpleSpectralAccess capability type called ProtoSpectralAccess
• lots of clarified documentation
• removed complianceLevel, defaultMaxRecords, maxAperture from ProtoSpectralAccess
• reinstated supportedFrame element
• fixed typo in value for creationType: specialExtraction -> spectralExtraction
• maxFileSize: required units changed from bytes to kilobytes for consistency with SSA interface

SSA-v0.1.xsd

This is a working draft version for current use in the Registry.
an example

Barring any further comments, the top schema will become SSA-v0.2.xsd and supercede the top one.

SSA Extension metadata

Here is a list of the extension metadata that can be included in an SSA schema:

complianceLevel

The category indicating the level to which this instance complies with the SSA standard. Allowed values are "query", "minimal", and "full":

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.

This level represents the lowest level of compliance.

minimal

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

This level represents the middle level of compliance.

full

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

This level represents the highest level of compliance.

dataSource

The category specifying where the data originally came from. Allowed values are "survey", "pointed", "custom", "theory", "artificial". (See schema for definitions of values.)

creationType

The category that describes the process used to produce the dataset. 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. Allowed values are "archival", "cutout", "filtered", "mosaic", "projection", "spectralExtraction", "catalogExtraction" (See schema for definitions of values.)

maxSearchRadius

The largest search radius, in degrees, that will be accepted by the service without returning an error condition.

maxRecords

The hard limit on the largest number of records that the query operation will return in a single response

defaultMaxRecords

The largest number of records that the service will return when the MAXREC parameter not specified in the query input.

maxAperture

The largest aperture that can be supported upon request via the APERTURE input parameter by a service that supports the special extraction creation method.

maxFileSize

The maximum image file size in bytes.

testQuery

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

Note that there are planned changed to VODataService, including a general test query metdatum that will supercede the testQuery item above.

Representing v1.0 and pre-1.0 implementations

One important issue we need to address is how to support the earliest SSA implementations. These were built well before v1.0 of the SSA spec was completed; thus, it is unlikely that they would be compliant at this time. Still, several do exist, and it would be good to recognize these as serving spectra.

The subsection below gives a proposal for representing the pre-v1.0 services with a special version value on the interface. However, the editor of the SSA spec voiced a preference for labelling pre-v1.0 implementations using a different capability xsi:type, and there were no dissents. Thus, in the new schema above, there is a second capability type (defined identically to the first one) called "ProtoSpectralAccess" (as oppsed to "SimpleSpectralAccess").

Previous version proposal

VOResource v1.0 allows one to list in one resource description support for different versions of a protocol. For SSA, this means that within the "SimpleSpectralAccess" capability element, multiple interface elements may be listed, each with a different value for its version attribute. (If version is not provided, "1.0" is to be assumed.)

I recommend that we encourage the registration of the early SSA services using the "SimpleSpectralAccess" capability but to set the value of the interface element to "proto". That is,

   <ri:Resource ...>
      ...
      <capability xsi:type="ssa:SimpleSpectralAccess">
         <interface xsi:type="vs:ParamHTTP" version="proto">
            <accessURL> ... </accessURL>
         </interface>
         ...
      <capability>
      ...
   </ri:Resource>

(If you don't "proto" as a version string, please suggest an alternative, e.g "0.5".)

-- RayPlante - 24 Sep 2007