resuming progress on TAP

[Patrick Dowler]

On Sunday 08 February 2009 19:27:19 Robert Hanisch wrote:
> We can tweak the presentation, but it is essential, I think, to present
> ADQL and PARAM together as alternative query languages, just as Pat has
> very nicely described.  ADQL is required, PARAM is optional.  This was
> agreed in Trieste.

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.

> Francois and Markus have raised some important technical questions.  These
> need to be addressed and resolved.  

I think this would also (potentially) address one of the issues raised by 
Markus: param-query can be a pretty complex thing and we may benefit from 
thinking about it and specifying it explicitly. It is easy to think of 
param-query as a simple thing, but in many ways it provides a higher level of 
abstraction that ADQL and I feel it deserves careful thought and design.

This would decouple the TAP and param-query specs, allowing each to move 
forward at whatever pace can be sustained. It would result in a single TAP 
specification and there would be no particular need to make a new version 
once param is complete. It would also benefit other DAL service 
specifications to have a common spec for param query that can be referenced  
rather than just copying it from one service spec to the next.

-- 

Patrick Dowler
Tel/Tél: (250) 363-0044
Canadian Astronomy Data Centre
National Research Council Canada
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