[TAP] sync vs async
gtr at ast.cam.ac.uk
Fri Mar 6 02:53:17 PST 2009
There seem to be two memes emerging from recently responses.
The first is that parametric query is somehow more fundamental than
The second is that parametric query is robust while ADQL is fragile. I
don't think either of these ideas are quite right.
We know that ADQL is more general than the parametric query and it
less data model than parametric query with POS and SIZE. I think this
the ADQL service more fundamental. If a site offered a partial TAP
just ADQL I could write a parametric-query service that delegated to
without having a copy of the database. (This may be a useful tactic
for NVO if
there arise TAP sites that don't provide the parametric query.) I
couldn't do it
the other way round.
As to fragility, there's no reason why an ADQL service should be more
a parametric service. It's the synchronous services that are fragile,
parametric interface can be asynchronous if it needs to be.
If I wanted to build an application - perhaps part of a portal - that
queries, I would need to build it on asynchronous queries, so that it
consistently, and I would probably need ADQL. (Consider the case of a
that selected on high B-V OR high V-K; you can't say that in the
because there's no OR operator. Or consider a query that needs joins.)
This is not a request to change TAP. I just ask that we recognize
and asynchronous queries are important to building everyday systems for
astronomy. They are not baroque toys.
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