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Subject: Comments on WS-RA WS-MetadataExchange draft


Hi,

the following is a first set of comments on the WS-RA 
WS-MetadataExchange draft.

Section 7: This section is new (compared to the version referenced by 
DPWS 1.0, not compared to the submission), and it provides a way to 
attach metadata to an EPR. I think this could be a valuable feature to 
use in DPWS metadata, specifically for helping distinguishing between 
endpoints exposed by hosted services (a typical use case is the need to 
expose one BP1.1-compliant and one DPWS-compliant EPR for each hosted 
service).

Ideally, there should be an easy way to directly attach an endpoint 
effective policy (as defined in WS-PolicyAttachment) to the EPR, in 
order to bypass the usual complex algorithm that the client must 
implement to compute the endpoint effective policy, and which is not 
practical for some embedded clients:
1) Download the WSDL
2) Retrieve the service port corresponding to the EPR (matching the 
address, and hoping that the WSDL is complete, i.e. is dynamically 
generated by the service to contain an up-to-date address, which is 
often numerical in cases of devices).
3) Build the endpoint effective policy by merging info extracted from 
the WSDL and possibly an external policy document.

The closest way I can see in the current proposal would be to use an 
external policy attachment as metadata section, using the EPR as policy 
scope. So for instance, to express that an EPR supports the DPWS 
requirements for hosted services, one could have:

<wsa:EndpointReference
    xmlns:wsa='http://www.w3.org/2005/08/addressing'>
  <wsa:Address>http://192.168.0.34/myHostedService</wsa:Address>
  <wsa:Metadata>
    <mex:Metadata xmlns:mex='http://www.w3.org/2009/09/ws-mex'>
      <mex:MetadataSection xmlns:wsp='|http://www.w3.org/ns/ws-policy|'>
          Dialect='http://www.w3.org/TR/ws-policy-attach'>
        <wsp:PolicyAttachment>
          <wsp:AppliesTo>
            <wsa:EndpointReference>
              <wsa:Address>http://192.168.0.34/myHostedService</wsa:Address>
            </wsa:EndpointReference>
          </wsp:AppliesTo>
          <wsp:Policy>
            <dpws:Profile xmlns:dpws='http://docs.oasis-open.org/ws-dd/ns/dpws/2009/01'/>
          </wsp:Policy>
        </wsp:PolicyAttachment>
      </mex:MetadataSection>
    </mex:Metadata>
  </wsa:Metadata>
</wsa:EndpointReference>

A simpler solution could be to have (assuming that the EPR defines a 
default policy scope):

<wsa:EndpointReference
    xmlns:wsa='http://www.w3.org/2005/08/addressing'>
  <wsa:Address>http://192.168.0.34/myHostedService</wsa:Address>
  <wsa:Metadata>
    <mex:Metadata xmlns:mex='http://www.w3.org/2009/09/ws-mex'>
      <mex:MetadataSection xmlns:wsp='|http://www.w3.org/ns/ws-policy|'>
          Dialect='http://www.w3.org/TR/ws-policy'>
        <wsp:Policy>
          <dpws:Profile xmlns:dpws='http://docs.oasis-open.org/ws-dd/ns/dpws/2009/01'/>
        </wsp:Policy>
      </mex:MetadataSection>
    </mex:Metadata>
  </wsa:Metadata>
</wsa:EndpointReference>

or even better (allowing any predefined dialect to appear in the 
metadata, as in a Get response)

<wsa:EndpointReference
    xmlns:wsa='http://www.w3.org/2005/08/addressing'>
  <wsa:Address>http://192.168.0.34/myHostedService</wsa:Address>
  <wsa:Metadata>
    <wsp:Policy>
      <dpws:Profile xmlns:dpws='http://docs.oasis-open.org/ws-dd/ns/dpws/2009/01'/>
    </wsp:Policy>
  </wsa:Metadata>
</wsa:EndpointReference>


Editorial comments:
It seems that the namespace used in schema import elements in several 
examples should be http://services.example.org/stockquote/schemas 
instead of http://services.example.org/stockquote

Cheers

Antoine



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