SSA extension schema

[Ray Plante]

Registry providers and SSA enthusiasts,

One of the things we'll talk about this week in Cambridge is support
SSA services in the registry.  I've been discussing an VOResource
extension for SSA with Doug Tody and Markus Dolensky.  There is draft
schema being considered; however, there are still some issues to be
worked out.  Nevertheless, there is quite a bit of demand to support
current SSA implementations in the registry as soon as possible.

I've set up a twiki page for discussion of this schema.

http://www.ivoa.net/twiki/bin/view/IVOA/SsaResourceSchema

You will find two versions of the schema on that page:  one that has
all of the elements that are currently desired in the extension,
including those that still need further discussion and consideration.
The second is a working draft being put forward for immediate
support which has the unstable bits removed.  If we adopt this version
now, it is expected that we would migrate to a final 1.0 version in 3
to 6 months.

One important issue we need to address is how to support the earliest
SSA implementations.  These were built well before v1.0 of the SSA
spec was completed; thus, it is unlikely that they would be compliant
at this time.  Still, several do exist, and it would be good to
recognize these as serving spectra.

VOResource v1.0 allows one to list in one resource description support
for different versions of a protocol.  For SSA, this means that within
the "SimpleSpectralAccess" capability element, multiple interface
elements may be listed, each with a different value for its version
attribute.  (If version is not provided, "1.0" is to be assumed.)  I
recommend that we encourage the registration of the early SSA services
using the "SimpleSpectralAccess" capability but to set the value of
the interface element to "proto".  That is,

    <ri:Resource ...>
       ...
       <capability xsi:type="ssa:SimpleSpectralAccess">
          <interface xsi:type="vs:ParamHTTP" version="proto">
             <accessURL> ... </accessURL>
          </interface>
          ...
       <capability>
       ...
    </ri:Resource>

(If you don't "proto" as a version string, please suggest an
alternative, e.g "0.5".)

cheers,
Ray