VO and ADEC identifiers

[Patrick Dowler]

On Thursday 18 September 2003 12:36, Tony Linde wrote:
> If there is a single service which sits in front of a collection of
> datasets, each of which is a table within a database, how does a query
> sent
> to the service work? Does it query every dataset with the same criteria?
>
> Are all the datasets just blocks within a single table so that a query
> is
> effectively on the colleciton as a whole and the data returned can be
> from
> many datasets?
>
> If a user queries the registry looking for a service which can provide
> data
> of some description, how is the collection of datasets described under a
> single service? - ie does the metadata (coverage, content etc) embrace
> all
> the datasets as if they all existed in a single table?
>
> Sorry if this is AstroInformatics 101 :)

"dataset" is a heavily (over-)used word. To some people it means one or more
related files from a telescope or archive (1+ images). To another, the whole 
SDSS source catalog is a dataset (ie. many RDB tables).  There are cases 
where a "dataset" is a set of images, spectra, and a source catalog to go 
with it. I think the confusion comes from the fact that "data" is (over-)used
to mean both the observational data (images, spectra, time series, etc) and
the derived or extracted information (source catalogs, for example). 

Whether the use of data and dataset if over-use can be argued until the end of 
time. It certainly is a vague concept in practice and in my experience even 
individuals tend to use it losely and differently (which doesn't help :-).

-- 
Patrick Dowler
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