Charac Answer

[Anita Richards]

> 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.

Arnold, I am not saying that any meta data should not be available.  But 
very often I just want to get an image or a spectrum and to know what the 
resolution is, roughly how accurate the calibration is etc.  I will simply 
not bother if I ahve to read many pages of explanation which will 
inevitably be in jargon.  As a data provider I know very well that you 
have to offer layers.

Providing too much information up front is extemely counterproductive, 
people think that you ahve to be an expert radio astronomer to begin to 
look at the data.  Wha is necesary is to have a heriachical apporach.  In 
my vire the Char model should just contain as much information as is 
necessary to supply a well-described data product.  If the user wants more 
information they should have a link to the Provenance or Observation or 
whatever.  Similarly, the Registry needs to know whether a particular data 
collection covres a certain bit of the sky, but retrictions on an archive 
due to the geographic location of the observatory cshould have been 
translated into sky limits for a registry entry.

> 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.

But that does not mean that it all has to be in one monolithic model!

> 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.

Absolutely, which is why we need to have discrete but mutually compatible 
models which describe things at the appropriate level of detail.


> 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.

But attatch it _where_? That is all I am arguing, that the VO will never 
implement anything properly if we make it too unwieldy.  Moreover we will 
only get all the details of models right if we test them againsst users' 
needs. As a one-time radio astronomer shurely you remember a certain 
software project which tried to be all things to all astronomers....

I am really concerned that it is time to stop adding bits to existing 
models, since many of them duplicate - or rather, nearly-but-not-quite 
replicate bits of other models - and start using them. I agree completely 
that we attach all metadata but Charactersation is intended to be a _part_ 
of a larger model, not replace STC, the Regsitry and goodness knows what 
else.

> 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.

That is why we need both!

STC is to me a reference manual.  If the VO (or indeed internal 
observatory data models) wwant to describe anything covered by STC then it 
shuld be conformant.  But e.g. prople designing registry interfaces for 
data providers are putting effort into only presenting selected defaults 
relevant to a type of data - the operative word being default, just as 
with Vizier, yuo can 'view all fields' if you want, but the VO is supposed 
to be able to deduce intelligent defaults as a first offering.


I don;t really care if we include observatory location or not, but I don't 
that that is what we are arguing abojt, it is indeed the 'different 
approach.  What I do care very strongly and negatively about, is adding 
location, and something else, and, andd,and.... never getting finished or 
having something which no-one has the time to impliment.


cheers
a