resuming progress on TAP

[Douglas Tody]

On Tue, 10 Feb 2009, Keith Noddle wrote:

>> One way to approach this would be to follow the same strategy that the VOQL 
>> group did when separating ADQL and TAP: we could specify the "DAL 
>> parameter-based query language" in a separate document that goes through 
>> the standards process. It would be usable (referenced) by all DAL services. 
>> The TAP spec would refer to the ADQL spec as a required language and allow 
>> for use of other languages.
>> 
>> Mechanically, the TAP service metadata would have to describe which query 
>> languages and versions are supported, but we have to do that in any case.
> I agree. I like that it frees up the option to relatively easily add other 
> optional querying capabilities (XQuery for object databases/other XML data 
> resources, maybe?) at some point in the future.

The draft TAP spec already provides for alternate query languages:
the LANG parameter, which could be used to specify native SQL or maybe
XQuery - in general any syntax which behaves relationally and returns
a table result.  Indeed this is a nice feature, but it has nothing
to do with provision of parameter based queries for table access,
which are optimized for typical astronomical use cases.

 	- Doug