TAP information schema
greene at stsci.edu
Fri Oct 12 10:28:09 PDT 2007
Thanks for pointing out the requirements for fully qualified table names,
it appears to be a case of
oversimplification is the early presented usage.
I really am not clear on what your summary means in terms of how a client
will access the tap services.
I thought ADQL was to provide the query language specification for accessing
tap services, but maybe I'm
missing something in your point of accessing them through registry
A VORegistry persistence of service table names and columns are
theoretically available via the standard registry interface. This interface
can be queried as keyword or adql, thus I do not see how we are escaping the
issue of adql not handling
full db table schema name specifications unless we limit the query level.
From: owner-dal at eso.org [mailto:owner-dal at eso.org] On Behalf Of Patrick
Sent: Friday, October 12, 2007 1:03 PM
To: Undisclosed.Recipients :
Cc: dal at ivoa.net
Subject: Re: TAP information schema
It isn't really all that dire :)
The crux is that to use TAP the user needs to know the table name
unambiguously; in the db this is the fully qualified table name (FQTN for
short), which is $catalog.$schema.$table
For the purposes of TAP 1.0, it would be sufficient to say that the
metadata about tables an columns (which is what one needs for discovery
anyway) has to specify unique, unambiguous table names.
What we should be careful about is to make sure that we do not include any
semantic meaning in such FQTNs - just say they have to be unique within the
service and leave it at that. In MySQL there is one catalog, so FQTNs can be
reduced to $schema.$table in that case. In general one always has a default
catalog they are connected to, so any TAP service which keeps all the
in one catalog could do the same... others that expose multiple catalogs via
a single TAP (eg upload VOTables to a VOSpace and they are available in the
service) might want to do that or they might want to use a separate catalog;
that is defintely what I would do. Still others might have historically used
the catalog as the namespace (we do that in our sybase servers, eg), so
we would use FQTNs like $catalog..$table or $catalog.dbo.$table.
Summary: I think we could get away with just having 1+ opaque unique table
names in the VOResource metadata and TAP implementors can decide if they
to put something arbitrary and map it to their DB or they can just put their
real FQTN in there and not have to process the ADQL at all. We just have to
make sure this thing has no specific meaning (well, people will see and
it and make assumptions anyway, that's unavoidable) that ties us down later.
On 2007-10-12 01:08, Tony Linde wrote:
> I thought TAP was a mechanism for sending ADQL through to registered
> services. The various posts here sound like trying to solve perceived
> problems with ADQL and Registry in TAP: that IMHO is the wrong way round.
> TAP spec should simply be used to push ADQL to a service then you get the
> changes you want into ADQL and the Registry and TAP still works. If ADQL
> changed so that it supports qualified table names then, and only then,
> should you update TAP to support the new spec, not try to predict what
> might look like in the future. If OTOH you are saying no-one can possibly
> use ADQL as it stands and there is no point producing TAP based on the
> current ADQL spec then you should get ADQL changed first, but I really do
> not think that is the case.
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