multiple capabilities of the same kind

[Paul Harrison]

Hi,

We have recently come across people wanting to register services with  
multiple capabilities of the same kind e.g. a resource with two  
capabiities whose standardID="ivo://ivoa.net/std/SIA", and this is a  
reasonable thing to want to do given that either the VOResource  
schema, nor the http://www.ivoa.net/Documents/latest/VOResource.html  
standard explicitly prohibit this use. However, my recollection of the  
intention when designing capability is that  a resource should have  
only a single capability of a particular kind (although multiple  
capabilities of different were of course central to the design).  
Because there was only to be a single capability of a particular kind  
there is only the standardID as the "key" that can be used to identify  
the particular capability within the resource, and consequently for a  
resource ivo://org.mytelescope/survey that has two capabilities with  
standardID="ivo://ivoa.net/std/SIA" it is impossible in software to  
reference which simple image access service is required.

I think we need to rectify this before the V1.0 schema goes into  
widespread use, and as I see it we have 2 possibilities;

EITHER

We amend http://www.ivoa.net/Documents/latest/VOResource.html to make  
it clear that only one resource is supposed to have only one  
capability of a particular kind (= standardID attribute value), and  
the above use case it achieved by simply registering two resources.

OR

We amend the VOResource schema and add an extra "name" attribute onto  
the capability element, which could be used to distinguish between  
multiple capabilities with the same standardID by using the value of  
the name attribute as the URI "fragment" e.g. ivo://org.mytelescope/ 
survey#rband could be used to identify the individual simple image  
access capability within the resource.


Paul.

Dr. Paul Harrison
JBCA, Manchester University
http://www.manchester.ac.uk/jodrellbank