Re: Response to TAP presentations

From: Keith Noddle <ktn-at-star.le.ac.uk>
Date: Thu, 17 May 2007 03:56:16 +0100

Hi Doug,

> I could probably agree with all of your points except for the following:
I'm really keen that we use what we have wherever possible. However, I also recognise the need to make everyone's lives as easy as possible - that way lies adoption of the VO! I am further convinced that consistent access to resource metadata - wherever and whatever their type - is vital and will become more so as time passes. How about this as a compromise:

1. TAP mandates that services return their metadata in VOResource format using the mechanisms defined in the VOSI
2. TAP mandates that the service ALSO returns those metadata in VOTable format in response to a metadata query

Given the formats will be so similar, the burden on the service developer will be reasonably light - hopefully a simple XSLT translation will do the trick. I know we tend to try to avoid mandating too much, but in this case, I think there is justification.

>
> On Thu, 17 May 2007, Keith Noddle wrote:
>

>>> (5) Tables and table metadata are both tables, and the IVOA has adopted a
>>> standard representation for tables, it is called VOTable. I believe VOTable
>>> should be the principle way that relational schema and the table data should
>>> be returned from TAP, although other formats may be offered by implementers.
>>> Because tables and table metadata are unified, it means that querying the
>>> table metadata is no different from querying table data itself.
>> How ever the metadata are returned, the results will have to have some format.
>> VOTable is XML as is VOResource and the VODataService extension. Given the
>> returned VOTable will contain exactly the same information as defined by
>> VODataService, why are we suggesting that IVOA defines yet another format
>> (schema) to apply to the returned VOTable? VOTable is designed to return data;
>> I am not convinced it is optimised to return medatata. Let's use what we have.

>
> The client application already has to support VOTable as the
> default output format for table data queries. If native XML
> (VOResource/VODataService) is the only format for table metadata (which
> appears to be the suggestion here) then a client has to be prepared
> to accept two completely different delivery formats for table data
> and metadata, despite the fact that both are fundamentally the same,
> i.e., tabular in nature. I think this is an unnecessary complication
> and would break the elegant relational approach, with a uniform
> interface for both table data and metadata, already demonstrated by
> the SQL information_schema. Since TAP is mainly about ADQL/SQL and
> relational queries, this would be a serious step to take.
>
> - Doug
>

Keith.

-- 
Keith Noddle                    Phone:  +44 (0)116 223 1894
AstroGrid Project manager       Fax:    +44 (0)116 252 3311
Dept of Physics & Astronomy     Mobile: +44 (0)7721 926 461
University of Leicester         Email:  ktn-at-star.le.ac.uk
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Received on 2007-05-17Z04:56:56