Minutes MWG 2003-09-25

[Clive Page]

On Thu, 2 Oct 2003, Tony Linde wrote:

> The preference for XQuery is that of a few people in AstroGrid; it is not a
> project policy although our current registry implementation is built that
> way.

I think I may be one of those few, so just a few words.  I agree with Roy
Williams that the registry will have more than a simple structure, and
I've argued that it's inherently hierarchical, with 3 or even 4 levels,
e.g.

Level 1:  site e.g. CDS, GSFC, STScI, etc
Level 2:  service, e.g. Vizier, Aladin, Astrobrowse, Skyview...
Level 3:  metadata on data tables (for table-based services) or images
Level 4:  column metadata in those tables, if required

Of course the registry can be represented as tables in a relational
database, or in a hierarchical database, such as an XML-based one.  If the
data volume is modest, the latter seems a natural choice, in which case
Xquery is a good query language for it.  By suitable software contortions
we could use SQL on an XML database, or Xquery on a relational one, but
that's somewhat less natural.  We ought to design to suit the
functionality required, and my feeling is that we haven't pinned this down
firmly enough yet.  So I'm not sure that Xquery is right, it just looks
more natural to me at the moment.


-- 
Clive Page
Dept of Physics & Astronomy,
University of Leicester,    Tel +44 116 252 3551
Leicester, LE1 7RH,  U.K.   Fax +44 116 252 3311