Resource Identifiers and Resource Type Identifiers

As the VO grows bigger it likely that we will be deploying several instances of the same type of service. There are two cases that I can think of

1. failover - where the service instances would be idential clones
2. same functionality, different algorithms - e.g. there could be several services providing photometric redshifts

In both these cases if writing code to hunt the registry there needs to be a way of hunting for specific instances of service as well as being able to search for types or classes of service.

In the schema it seems that the vr:Identifier for a vr:ServiceType fulfils the role of uniquely specifiying a service instance, however in the case of specifying the type of a service the situation appears to be more ambiguous.

There are;

vr:LogicalIdentifier
vr:RelatedResource
vr:Capability

each of which could conceivably be used to specify the "type" of the service. I am interested to gather opinions about this from the community, as I think it would be good to have a convention (that could perhaps be enshrined by making the schema more strict on one of the above elements) for identifying service types. Since, as mentioned above (and has already recognised in the case of UCDs), it is essential to have well defined names for types to be able to write software more easily.

-- 
Dr. Paul Harrison, Astrogrid Programmer
MERLIN/VLBI National Facility, University of Manchester,
Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, U.K.
tel +44 (0)1477 572681 (direct), 571321 (switch) - 07904025192 (mobile).