Notes from the TAP/ADQL splinter session on
Wednesday 21 May 2014 at the
IVOA Interop meeting at ESAC.
During the meeting the group reviewed a number of proposed changes to TAP and
ADQL described in the
TAP Implementation Notes Version 1.0.
The following section lists the recommendations agreed at the meeting for each of the changes that were reviewed.
After each section there is a table for adding feedback. Please add your vote to indicate
- +1 You agree with the decision
- 0 You don't mind either way
- -1 You disagree with the decision
If you vote to disagree please provide a brief explanation describing why (or a link to a new page if you prefer).
If you feel that an item needs more discussion please feel free to raise it on the working group
mailing list.
Thank you for your feedback. --
DaveMorris - 2014-09-04
Example item
Some text describing the item, with a reference to the original item in the TAP Implementation Notes.
May 2014 Interop
A brief summary of the discussion at the May Interop.
Community feedback
| Name |
date |
vote |
notes |
| MarcoMolinaro |
2014-09-04 |
+1 |
Yes, good idea |
| DaveMorris |
2014-09-04 |
0 |
Ok, as long as it is optional |
| DaveMorris |
2014-09-04 |
-1 |
It isn't the right colour, our users prefer blue background. |
Separator Nonterminal
This
item proposes two options to clarify the use of whitespace and comments in
ADQL.
One option for such a clarification is to amend section 2.1 of
std:ADQL with a subsection 2.1.4, "Tokens and literals", containing text like the following (taken essentially from
std:SQL1992).
- Any token may be followed by a separator. A nondelimiter token shall be followed by a delimiter token or a separator.
Since the full rules for the separator are somewhat more complex in
std:ADQL, an attractive alternative could be to omit the separator nonterminal from the grammar and to just note:
- Whitespace and comments can occur wherever they can occur in std:SQL1992.
May 2014 Interop
Accepted as errata -
It was agreed that this item should be included in the errata note for the current,
std:ADQL-20081030, version of the standard.
Community feedback
| Name |
date |
vote |
notes |
| DaveMorris |
2014-09-04 |
+1 |
Happy with either option |
| MarcoMolinaro |
2014-09-17 |
+1 |
Prefer the II solution |
| |
|
|
|
Type System
This
item proposes adding new section to introduce a notion of types into section 2 of the
std:ADQL standard.
See
original text for details of the proposed type mappings.
[TODO insert table here]
May 2014 Interop
Accepted for next version -
It was agreed that this item should be discussed further, with a view to including it in the next (minor) version of the
std:ADQL standard.
Community feedback
| Name |
date |
vote |
notes |
| DaveMorris |
2014-09-04 |
+1 |
Yes, but needs some clarification (see below). |
| MarcoMolinaro |
2014-09-17 |
+1 |
|
| |
|
|
|
Transporting
TIMESTAMP,
POINT and
REGION as strings should
not imply the
ADQL string concatenation operators are applicable.
--
DaveMorris - 2014-09-04
(Dave, you mean
BLOB or
CLOB? --
MarcoMolinaro - 2014-09-17)
(Edited to remove
BLOB --
DaveMorris - 2014-09-18)
Empty Coordinate Systems
This
item proposes
deprecating the string-valued first argument for the geometry constructors (
BOX,
CIRCLE,
POINT,
POLYGON).
May 2014 Interop
Requires further discussion -
It was agreed that the proposal needs more work done on it before it could be included in the
std:ADQL standard.
Community feedback
Explanation of optional features
This
item proposes
adding a section of text to both the
std:TAP and
std:ADQL specifications that clarifies how optional features are described.
May 2014 Interop
Accepted for next version -
It was agreed that this item should be discussed further, with a view to including it in the
next (minor) version of the
std:ADQL standard.
Community feedback
Simple Crossmatch Function
This
item proposes
adding a simple positional crossmatch function to
std:ADQL.
May 2014 Interop
Requires further discussion -
It was agreed that the proposal needs more work done on it before it could be included in the
std:ADQL standard.
- It was agreed that this would be a useful feature for end users
- It was noted that adding this feature could be difficult to implement
- It was noted that part of the rationale for the IVOA services was to implement difficult things on the server side, making things easier for the end user
Community feedback
No type-based decay of INTERSECTS
This
item proposes
deprecating the use of POINT as the first parameter to INTERSECTS.
May 2014 Interop
Accepted for next version -
It was agreed that the proposed text should be included in the next (minor) version of the
std:ADQL standard.
Community feedback
Generalized user defined functions
This
item proposes
allowing user defined functions to return geometric types.
May 2014 Interop
It was agreed that there should be no restriction on the return types of User Defined Functions.
Accepted as errata -
It was agreed that this should be included in the errata note for the current,
std:ADQL-20081030, version of the standard.
Futher discussion -
It was also noted that the
SimDAL working group would like to be able to define table value functions in
std:ADQL.
It was agreed to continue the discussion to find a way of adding support for table value functions in a future version of the
std:ADQL standard.
Community feedback
Case-Insensitive String Comparisons
This
item proposes
adding functions and operators for to support case-insensitive string comparisons.
May 2014 Interop
Accepted for next version -
This item was discussed by members of the working group at the May 2014 IVOA Interop meeting.
It was agreed that the following functions should be included as an
optional feature in the
next (minor) version of the
std:ADQL standard.
It was agreed that the following operator should be included as an
optional feature in the
next (minor) version of the
std:ADQL standard.
Community feedback
Set operators
This
item proposes
adding support for the
UNION,
EXCEPT and
INTERSECT operators.
May 2014 Interop
Accepted for next version -
This item was discussed by members of the working group at the May 2014 IVOA Interop meeting.
It was agreed that the following operators should be included as
required operators in the next
(minor) version of the
std:ADQL standard.
It was agreed that the text describing the set operators in the
std:ADQL standard should
include the following caveats.
- The set operands MUST produce the same number of columns
- The corresponding columns in the operands MUST have the same data types
- The corresponding columns in the operands SHOULD have the same metadata
- The metadata for the results SHOULD be generated from the left-hand operand
Community feedback
| Name |
date |
vote |
notes |
| DaveMorris |
2014-09-04 |
-1 |
I agree with the proposal (+1), but we need to confirm which platforms support what operators (see below) |
| MarcoMolinaro |
2014-09-17 |
+1 |
|
| |
|
|
|
The Oracle database platform includes support for
UNION and
INTERSECT, but not
EXCEPT.
However, Oracle's
MINUS operator appears to be equivalent to
EXCEPT.
If we make these operators as a required feature of
std:ADQL
then it means service implementations based on Oracle will have to
parse and translate
ADQL queries.
This may not be an issue, but it will be the first time we have (knowingly) added
a feature to
std:ADQL that requires service implementations to
parse and translate
ADQL queries.
--
DaveMorris - 2014-09-04
Please contribute your knowledge to the table below to help us build a map of which
platforms support which operators.
| Vendor |
version |
UNION |
INTERSECT |
EXCEPT |
verified by |
| SQLServer |
|
YES |
YES |
YES |
DaveMorris - 2014-09-04 |
| Sybase |
|
|
|
|
|
| Oracle |
|
YES |
YES |
(see below) |
|
| PostgreSQL |
|
YES |
YES |
YES |
|
| MySQL |
|
YES |
NO |
NO |
MarcoMolinaro - 2014-09-17 |
| Derby |
|
|
|
|
|
| HSQLBD |
|
|
|
|
|
| SQLLite |
|
|
|
|
|
Oracle - The Oracle database platform supports the
UNION and
INTERSECT,
operators directly, and the
MINUS operator is equivalent to
EXCEPT.
MySQL - The
MySQL DBMS doesn't support
EXCEPT and
INTERSECT. Query translations are needed in both cases.
Adding a Boolean Type
This
item proposes
adding a BOOLEAN type to
std:ADQL.
May 2014 Interop
Requires further discussion -
This item was discussed by members of the working group at the May 2014 IVOA Interop meeting.
It was agreed that although making these changes would be a good thing, more work needs to be
done on identifying and solving potential compatibility issues before the changes can be
included in the
std:ADQL standard.
- It was agreed that BOOLEAN data type would be a useful feature to add
- It was agreed that changing the return type of CONTAINS() to be a BOOLEAN would make it easier to use
- It was agreed that making these changes could cause compatibility issues which could not be addressed in a (minor) increment of the std:ADQL standard
- It was agreed that both of these changes should be considered for a future (major) increment of the std:ADQL standard
Based on the points raised at the May 2014 Interop we would like to split this into two separate proposals
and ask for your feedback on each proposal.
Adding a Boolean Type
The first proposal is to add support for a BOOLEAN type to
std:ADQL,
without changing the return type of CONTAINS().
This would avoid the potential compatibility issues raised at the May 2014 Interop.
The general concensus at the May 2014 Interop was that a BOOLEAN data type would be useful,
and that adding it as a new type would not cause compatibility issues.
Community feedback
changing the return type of CONTAINS()
The second proposal is to change the return type of CONTAINS().
This is the part that would potentially cause compatibility issues
with existing services and clients.
Community feedback
Casting to Unit
This
item proposes
adding a new function
IN_UNIT(expr, ) which would convert values in one unit into another.
May 2014 Interop
Requires further discussion -
It was agreed that the proposal needs more work done on it before it could included in the
std:ADQL standard.
- It was agreed that scaling conversions would not be difficult to implement
- It was agreed that conversion between wavelength and frequency would be difficult to implement consistently
- It was agreed that unit conversions would be most useful in a SELECT list
- It was agreed that unit conversions would be most difficult to implement in a WHERE clause
Community feedback
Column References with UCD Patterns
This
item proposes
adding a pre-processing macro that locates columns based on their UCD.
May 2014 Interop
Requires further discussion -
It was agreed that the proposal needs more work done on it before it could be considered ready
to be included in the
std:ADQL standard.
Community feedback
Modulo operator
This
item proposes
adding the modulus operator
x % y to the
std:ADQL grammar.
May 2014 Interop
Rejected -
It was agreed that the benefits of adding the
x % y operator syntax were outweighed by cost of
compatibility issues caused by adding a new
required operator to the
std:ADQL grammar.
Community feedback
| Name |
date |
vote |
notes |
| DaveMorris |
2014-09-04 |
+1 |
Disclosure - this is one of mine and I'm sneaking it back in (see below) |
| MarcoMolinaro |
2014-09-17 |
+1 |
|
| |
|
|
|
If this is the
only required operator we are adding, then it is probably not
worth the potential compatibility issues.
However, if we are updating the
std:ADQL grammar to add
UNION,
EXCEPT and
INTERSECT as operators,
does adding the
x % y operator cause any additional compatibility issues ?
--
DaveMorris - 2014-09-04
Bitwise operators
This
item proposes
adding support for the
AND,
OR,
XOR and
NOT bitwise operations and hexadecimal literals to the
[std:ADQL] grammar.
May 2014 Interop
Accepted for next version -
It was agreed that hexadecimal literal values should be included in the next (minor) version
of the
std:ADQL standard.
Accepted for next version -
It was agreed that the following functions should be included as an
optional feature in the
next (minor) version of the
std:ADQL standard.
-
BIT_AND(x, y)
-
BIT_OR(x, y)
-
BIT_XOR(x, y)
-
BIT_NOT(x)
Rejected -
It was agreed that the benefits of adding the operator,
[exp] op [exp], syntax for each operation
were outweighed by cost of compatibility issues caused by adding new operators to the
std:ADQL grammar.
However, if we are updating the
std:ADQL grammar to add
UNION,
EXCEPT and
INTERSECT as operators,
does adding the
[exp] op [exp] for each of the bitwise operations cause any additional compatibility issues ?
--
DaveMorris - 2014-09-04
Community feedback
| Name |
date |
vote |
notes |
| DaveMorris |
2014-09-04 |
+2 |
Please vote +1 to accept the functions, +2 to accept the operators |
| MarcoMolinaro |
2014-09-17 |
+1 |
|
| |
|
|
|
CAST operator
This
item proposes
adding a limited form of the
CAST operator to the
std:ADQL grammar.
This proposal specifically limited the
CAST operation to numeric data types only,
and excluded
CAST to and from character strings.
May 2014 Interop
Accepted for next version -
It was agreed that the CAST operator should be including as a required operator in the next
(minor) version of the
std:ADQL standard.
It was agreed that the set of type conversions should be discussed further, with a view to
finalizing the set of conversions supported in the next (minor) version of the
[std:ADQL] standard.
Community feedback
