IVOA Identifiers Working Draft

[Ray Plante]

Hi Tony,

On Fri, 12 Sep 2003, Tony Linde wrote:
> Referring to my previous email, Sa.CXO is a data collection and Sa.CXO/2900
> is a dataset.

I have pressed the question as to the role of the first field (e.g. 
"Sa.CXO").  The answer from Arnold and Tom (correct me if I'm wrong) is 
that this field is simply to establish a namespace.  Choosing the data 
collection (or more precisely, the facility from which the data 
originated) is a convenient way of dividing into namespaces.  It plays no 
other role in the resolving of the identifier.  Thus, it corresponds to 
our AuthorityID.

> To resolve Sa.CXO/2900, ADS would look up Sa.CXO in a registry (assuming
> Sa.CXO is a ShortName, perhaps?) to get the identifier of the data
> collection and would then use that identifier to find sky services which
> served that data.

Associating Sa.CXO with a data collection's ShortName is not a good idea, 
because there is no guarantee that it is unique and will consistantly 
refer to the same data collection.  This is exactly the role of an 
identifier: to be a unique reference.  

I'm confident that if we can resolve an ADEC identifier to a data 
collection registered in an IVOA registry, we can transparently return a 
service (or web page or other URL) for retrieving it.  The open questions 
are: how do we do that?  should we bother?  

There is also the separate but related question I posed:  Can an IVOA 
identifier exist for a resource that is not registered anywhere?  If so, 
what are the constraints (i.e. "as > long as ...")?

cheers,
Ray