TAP issues (fwd)

[Doug Tody]

---------- Forwarded message ----------
Date: Tue, 1 May 2007 17:37:31 -0400 (EDT)
From: Maria A. Nieto-Santisteban <nieto at skysrv.pha.jhu.edu>
Subject: TAP issues

Hi,

There are two KEY issues to the TAP protocol that I think the Tiger
team should be clearly specifying but so far I don't see this is
the case.  Pat mentioned them today and I think they deserve a lot
of attention.

1) How does the service say which ADQL constructs support and which not?

Considering that the ADQL CORE and EXTENSION concepts don't exist
any more and, as far as I know, it is not expected that all services
fully support the whole ADQL specification the question remains as

  - how does a user know whether or not the service is going to accept
    the query? Try and error?

[getCapabilities can probably deal with this, but we will still need
to specify someplace what these optional ADQL capabilities or UFNs are.
A schema metadata query would be another option for functions.  - DT]

2) What is needed to describe a TAP service so users/clients can do
decent queries in terms of content and performance?

In essence, how does the service describe tables, columns, indexes
and relationships?

I know you have been discussing the INFORMATION_SCHEMA standard
and some people don't find it adecuate. I got to agree that
INFORMATION_SCHEMA is not the full solution but without a question
is the right approach. The old skyNodes have tables describing
metadata. The missing parts were the relationships and indexes but
columns have information about UCDs, units, etc.

In my modest opinion, specifying the metadata schema is a fundamental
area where the tiger experts should focus their efforts. I would say
that finding out what is the necessary metadata information come
first. Later you can discuss how to make it available and decide
whether or not the VOResource schema can hold it.

Cheers

Maria
-- 
------------------------------------------------
Maria A. Nieto-Santisteban (nieto at pha.jhu.edu)
Johns Hopkins University
3400 N. Charles St.
Physics & Astronomy Department
Baltimore, MD 21218 (USA)

Tel: 	1 410 516-7679  Fax: 	1 410 516-5096