UCDS and DM and "Catalogue" tables

[Clive Page]

On Tue, 21 Oct 2003 posuna at iso.vilspa.esa.es wrote:

> I understand that people having data in X-Y tables do NOT want to hear
> about data models: they only want to be able to perform operations with
> the columns of their tables.

I'm not sure that's entirely true.  I think the problem is that three
partially overlapping groups of people have been trying over several years
to make sense of astronomical data, so they canclassify or organise it to
make data access simpler and more uniform.

(1) Those devising UCDs, which started out exclusively for tables in
VizieR.  I think it is now generally agreed that some hierarchical scheme
should replace the original flat namespace (though designed with
components which split naturally into layers).

(2) Those devising Data Models.  The problem for those outside this effort
is that there have been so many data models, different in structure and
detail, but all apparently equally valid.  I didn't manage to attend the
DM sesssion in Strasbourg, but am pleased to hear of serious convergence.

(3) Those devising query languages and data access routines, who need some
DM or UCD scheme to do the job properly, except for the serious problem
that a UCD does not lead to a unique column in some (many?) tables.

I thought that Tom's ideas at Strasbourg sounded good, and look forward to
seeing his proposal in print.  If it's true that there is now a single
agreed Data Model, does that not suggest that UCDs should be assigned on
the same hierarchical basis?


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