proposed VODataService changes

[Francois Ochsenbein]

Hi Ray,

I'm afraid the terms proposed (catalog, schema) have not the same
meaning for eprsons with astronomy background or IT background.
Details about what they mean would be quite useful. Also it
would be interesting to specify what's the scope of the elements
included in the <join>: can these refer to different catalogs ?

There are also some controversies about the TAP itself -- 
the TAP-reolated deinitions in the registry may therefore 
change in the near future...

Cheers, francois

>
>Hi RWGers,
>
>Today in Trieste, Aurelien will be (or is now) presenting some proposed
>changes to VODataService that are aimed at better support for TAP
>services.  Guy Rixon will be posting a revised XML Schema file to the
>twiki page, VODataService
>(http://www.ivoa.net/cgi-bin/twiki/bin/view/IVOA/VODataService).  Here are
>some initial comments on these changes.
>
>Just by way of summary, this proposed changes aim to:
>   o  indicate the database schema a table belongs to
>   o  the functions supported by the database
>   o  the columns that can be used to join tables
>
>One of the complaints we've addressed in past VOResource schemas has been
>over deep XML hierarchies, so it would be worthwhile to examine if this
>can be reduced at all in this proposed schema.  There are two main reasons
>for avoiding deep hierarchies.  The biggest is that deep hierarchies are
>harder to map to relational model (as they tended to lead to a
>proliferation of tables that are difficult to understand by even a db
>administrator).  The second is that it can be more complicated getting
>information out of the hierarchy.
>
>There is at least one place I would recommend some flattening: I'm
>wondering if we really need to capture the database schema as a new
>element layer (<schema>) between a <catalog> and <table>.  Can we instead
>do something like this?
>
>    <catalog>
>      <name>The X survey catalog</name>
>      <description>...</description>
>      <table>
>         <schema>...</schema>
>         <name>...</name>
>         <description>...</description>
>         <column>...</column>
>         <column>...</column>
>         ...
>      </table>
>      <function>                      <!-- optional -->
>         <schema>...</schema>
>         <name>...</name>
>         ...
>      </function>
>      <join>                          <!-- optional -->
>         ...
>      </join>
>    </catalog>
>
>In this case, if the <schema> element is omitted, the default schema is
>assumed.
================================================================================
Francois Ochsenbein       ------       Observatoire Astronomique de Strasbourg
   11, rue de l'Universite F-67000 STRASBOURG       Phone: +33-(0)390 24 24 29
Email: francois at astro.u-strasbg.fr   (France)         Fax: +33-(0)390 24 24 32
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