datasets and registries

[Doug Tody]

On Fri, 19 Sep 2003, amicol wrote:

> In the end my basic questions are:
> 
> -What should I ask the registry to know which services
> can offer HST products ?

When each service is registered it should list the data collections which
it serves.  Note this could be zero, or a very large number.  It could
change with time, requiring that the registry entry be updated.

Then you just do a registry query to find all the services that serve a
particular data collection.  One might refine this further by the service
type, since there might be many ways of looking at a given type of data.


> -And what to ask to know which service can offer WFPC2 associations ?

Depends.  If the WFPC2 associations are precomputed they could be 
registered as a new data collection (sounds likely).  Otherwise you have
a service which returns a form of virtual data, or possibly an analysis
service.

Virtual data is a major new topic which has hardly been touched on here yet.
We discussed this a while back in NVO (it is coming up again now) and
decided that before one can describe virtual data, we needs to be able
to describe physical, static data products.  The recent discussion of
identifiers gives me renewed hope (ADEC helped a lot) that we will soon
be able to deal with persistent data, data replication, and eventually
characterization of virtual data.  Note that we already have services
which generate virtual data - an image cutout service for example does
this already.

 
> I sincerely thought that at whatever site we would always
> use ivo://NASA/HST<etc> because that is the UNIQUE identifier
> for HST datasets ...

This is my view as well.  This identifier should be a property of the
data itself, independently of how it is used within the VO.

    - Doug