More separation

[Doug Tody]

>From Tony:
> Do we need a term intermediate between service and interface? In my model, I
> had a service providing access to a data collection and assumed that such a
> service could be of the sub-types Ray mentions but that a single such
> sub-type service might be accessed in different ways, e.g. cgi or web
> service (or have an interactive interface). It was the latter that I thought
> could be a repeating group element in the service definition rather than a
> separate resource.

This separation of service and interface is what we have always had in mind
for DAL.  Ideally the basic functionality of the service can be available
via more than one interface, e.g., cgi or web service.  Some advanced
capabilities such as SSO authentication or ADQL might only be available
via a web service interface.  A service is not limited to serving up one
data collection, nor is a data collection available via only one service.

Doug