Charac Answer

[Arnold Rots]

I don't think I agree.
The data provider should not try to second-guess the needs of the
client.  What that means is that the metadata accompanying a dataset
should be as complete as possible.  It is up to the client to decide
what (s)he wants to use and what not.
In the specific case at hand, the optical astronomer will most likely
ignore the ObservatoryLocation (e.g., because (s)he has no software to
handle it, probably because it is unimportant to the client).  But a
comet observer who happens to be interested in the dataset would want
to know about that location.
In my view, we can't rely in the VO anymore on the implied defaults
"that are obvious to everyone", since our clients come from different
communities that have different notions about what is obvious.  Hence
it becomes dangerous to try to second guess our clients and the right
thing to do is attach all potentially relevant metadata.  If we don't
do that from the start, it will never happen and we'll get into
trouble half-way through.
And that is the philosophy behind STC: build a structure that ensures
that all potentially relevant metadata on the related spatial,
temporal, spectral, and redshift coordinate axes are provided with the
data.  Though I'll admit that that is different from the approach that
Characterisation has taken.

Cheers,

  - Arnold

Anita Richards wrote:
> 
> I take Arnold's point completely, I agree that it should be in the 
> Observation data model, but I am not sure that it is specifically part of 
> characterisation; for example, in interferometry, the resolution which 
> results from the telescope separation is the releveant measure to be in 
> Characerisation,; the actual telescope positions belong elsewhere, I 
> think.  We need to distinguish between whre models ned to be comprehensive 
> and where they need to serve specific purposes of accessibility.  If an 
> optical astronomer wants a radio image, s/he will not have the software to 
> cope with telescope positions and possibly neither will any VO intermediat 
> layer; that is the job of a specialist data provider.
> 
> In short, we do need extremely comprehensice models like STC but we also 
> need (consistent) specialised models which are not overloaded with 
> elements which they can get from elsewhere.
> 
> cheers
> 
> a
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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