[ogsa-wg] RE: Modeling State: Technical Questions

[Savas Parastatidis]

Dear all,

I think something needs to be clarified with regards to handling
multiple jobs with one message. The beauty of document-oriented
interactions is that you can do things like...

<job-details-request>
  <job-id>urn:ogsa:job:guid:bla-bla-bla-001</job-id>
  <job-id>urn:ogsa:job:guid:bla-bla-bla-010</job-id>
  <job-id>urn:ogsa:job:guid:bla-bla-bla-002</job-id>
  <job-id>urn:ogsa:job:guid:bla-bla-bla-029</job-id>
</job-details-request>

Or

<job-suspend-request>
  <job-id>urn:ogsa:job:guid:bla-bla-bla-002</job-id>
  <job-id>urn:ogsa:job:guid:bla-bla-bla-005</job-id>
  <job-id>urn:ogsa:job:guid:bla-bla-bla-008</job-id>
</job-suspend-request>

The schema for the above document can allow anything from 0 to N number
of <job-id> elements.

What WS-RF and WS-Transfer and REST are doing is require that each
message be directed to only one resource. As a result, when it comes to
defining groups of resources, additional resources (representing
collections) have to be created. Populating and managing the collections
require additional messages.

The WS-RF/Ws-Transfer/REST model is a special case of the
document-oriented model I described above...

<!-- just one resource all the time -->
<job-suspend-request>
  <job-id>urn:ogsa:job:guid:bla-bla-bla-002</job-id>
</job-suspend-request>

In the WS-RF/WS-Transfer case the job ID will have to be part of the
wsa:To (wsa -> WS-Addressing) header. In REST, it is the URI on which
the operations are called (if we are using HTTP and the HTTP verbs, then
the URI usually has the 'http' prefix).

An example, of a WS-Addresing EPR...

<my:MyEndpointReference> 
  <wsa:Address> urn:ogsa:job:guid:bla-bla-bla-002</wsa:Address>
</my:MyEndpointReference>

Please note that the address doesn't have to carry transport/transfer
specific semantics (i.e. it doesn't have to be an 'http' URI). The above
would require a registry look up if that's necessary or perhaps a P2P
network that will know how to direct the message to its destination
based only on the above information. The sender of the message may never
actually see the transport-specific address of the receiving service.

This means that a SOAP msg like the one bellow will have to be sent...

<soap:Envelope>
  <soap:Header>
    <wsa:To>urn:ogsa:job:guid:bla-bla-bla-002</wsa:To>
  </soap:Header>
  <soap:Body>
    <job:job-suspend-request />
  </soap:Body>
</soap:Envelope>

Well... it turns out that this can by the special case of a message that
looks like this...

<soap:Envelope>
  <soap:Header>
    <wsa:To>urn:ogsa:job:service:Newcastle-Job-Service</wsa:To>
    <!-- again... a registry lookup although
         http://ncl.ac.uk/job-service could have also been used -->
  </soap:Header>
  <soap:Body>
    <job:job-suspend-request>
     <job:job-id>urn:ogsa:job:guid:bla-bla-bla-002</job:job-id>
     <job:job-id>urn:ogsa:job:guid:bla-bla-bla-003</job:job-id>
     <job:job-id>urn:ogsa:job:guid:bla-bla-bla-004</job:job-id>
    </job:job-suspend-request>
  </soap:Body>
</soap:Envelope>

What WS-RF and WS-Transfer seem to be doing is to expose to the wire the
programming abstraction that most of us are used to (i.e. calling
methods on an object). As a result, systems based on a special case are
designed rather than the more general case. It's been our argument all
along that this may not be the most efficient way of designing systems
in general (perhaps in certain application domains the WS-RF/WS-Transfer
approach may be appropriate) but I am prepared to be corrected on this
:-)

Best regards,
--
Savas Parastatidis
http://savas.parastatidis.name