resuming progress on TAP

[Patrick Dowler]

On Monday 09 February 2009 18:09:46 Robert Hanisch wrote:
> > 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.
>
> Hi Pat.  I don't think this is quite the right parallelism.  What we did
> with VOQL was separate the language from the complex functions that were
> layered on the language.  TAP/ADQL and TAP/PARAM are just two variants of
> the query.  I'd really like to see them progress together.

On the contrary, ADQL is NOT part of the TAP spec at all. It is fully 
described in it's own spec and param-query is definitely NOT a variant of it. 
It is a completely different query language. The only commonality is that 
both lie on top of a relational table model (although param skips the 
relational bit by only allowing one table).

There are many orthogonal parts to TAP that they can and do share: metadata, 
output format, and the small set of DAL "query control" that fall outside the 
query itself (e.g. MTIME).

As it stands, TAP and ADQL do progress independently. ADQL is standardised 
now. If a new revision of that spec comes out, TAP services will be able to 
use it. I think we could profitably do the same with "DAL param query 
language" and it would be especially profitable because other DAL services 
could refer to that spec instead of copying it. 

On Monday 09 February 2009 20:29:16 Douglas Tody wrote:
> If I understand your suggestion correctly Pat, you are proposing
> that we drop param query from TAP and just have ADQL, with a separate
> discussion of parameter-based queries to be added externally, somehow

I am definitely NOT proposing we drop param-query. I am proposing that we 
write a specification for it and ratify it via the standards process. Then it 
can be used in DAL services, including TAP, just as ADQL is a standard and it 
can be used in services, including TAP. It is a pretty simple divide and 
conquer approach that worked well enough for ADQL. It would keep the TAP spec 
smaller and improve clarity. 

Sincerely,

-- 

Patrick Dowler
Tel/Tél: (250) 363-0044
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9E 2M7

Centre canadien de donnees astronomiques
Conseil national de recherches Canada
5071, chemin West Saanich
Victoria (C.-B.) V9E 2M7