Re: WS-MEX and putting undifferentiated MEX sections

  The MEX spec is pretty consistent in that it talks about the @Identifier 
attribute being optional on the MetadataSection element - but _if_ present 
that it must be some dialect specific value.  EVD follows this rule too. 
If we believe that its asking too much for the service to determine the 
@Identifier value for an incoming piece of metadata (so that, like your 
example shows, people can query by the @Identifier later on) then I would 
think it would asking too much for a client to do it too. Take the case of 
a generic MEX client that is trying to move metadata from one service to 
another - it might Get metadata w/o the @Identifier attribute but then its 
expected to add it before it did the Put. 
 
  What if we took a different approach.  What if we required the 
@Identifier attribute to always be present on a MetadataSection element 
_if_ the value is defined for that type of metadata.  So, in our world, it 
MUST always be present for wsdl, xsd, policy and evd.  However, 
@Identifier would still be optional for queries (GetMetadata/Dialect 
elements).  By this I mean, when someone does a GetMetadata they are free 
to leave it out of the query - it just means they don't care about its 
value.  However, the result MUST have the @Identifier set.  In other 
words, @Identifier is only optional on a MetadataSection element IFF the 
metadata type doesn't define how to calculate it - and in those cases its 
ALWAYS absent. 

  The only other option I can see is to remove @Identifier all together  - 
and if we really wanted people to be able to filter their queries then let 
them pass in an XPath expression on the GetMetadata - then they can filter 
by anything they want.  But that might be too big of a change.

thanks
-Doug
______________________________________________________
STSM |  Standards Architect  |  IBM Software Group
(919) 254-6905  |  IBM 444-6905  |  dug@us.ibm.com
The more I'm around some people, the more I like my dog.



Gilbert Pilz <gilbert.pilz@oracle.com> 
Sent by: public-ws-resource-access-request@w3.org
02/13/2011 03:46 PM

To
"public-ws-resource-access@w3.org" <public-ws-resource-access@w3.org>
cc

Subject
WS-MEX and putting undifferentiated MEX sections






Suppose a MEX-enabled service is presented with the following request 
(SOAP envelope omitted for brevity):

      <mex:PutMetadata>
         <mex:Metadata>
            <mex:MetadataSection Dialect="wsevd:EventDescriptions">
               <wsevd:EventDescriptions targetNamespace=
"http://www.w3.org/2002/ws/ra/test/scenario"
                                        xmlns:sce=
"http://www.w3.org/2002/ws/ra/test/scenario"
                                        xmlns:wsevd=
"http://www.w3.org/2011/01/ws-evd"
                                        xmlns:xs=
"http://www.w3.org/2001/XMLSchema">

                  ...

               </wsevd:EventDescriptions>
            </mex:MetadataSection>
         </mex:Metadata>
      </mex:PutMetadata>

Notice how the above request does NOT contain an @Identifier on the 
MetadataSection element. As far as I can tell, this is both schema valid 
and spec conformant (the language of Section 6.3 PutMetadata seems to hint 
that both @Dialect and @Identifier are expected, but nowhere does it state 
that @Identifier is required).

You can probably guess where this is going; what if, subsequent to this 
request, you receive the following request

      <mex:GetMetadata>
         <mex:Dialect Type="wsevd:EventDescriptions"
                      Identifier="
http://www.w3.org/2002/ws/ra/test/scenario"
                      Content=
"http://www.w3.org/2011/01/ws-mex/Content/Metadata"/>
      </ws:GetMetadata>

The issuer of such a request might reasonably expect to receive the 
EventDescriptions from the previous PutMetadata operation, but how is the 
MEX implementation supposed to know that the @Identifier for the EVD 
(supplied in the PutMetadata) is 
"http://www.w3.org/2002/ws/ra/test/scenario"? You could build handlers 
that recognize various @Dialect values and know how to pull the relevant 
identifier out of the metadata itself, but this isn't a tractable general 
solution.

I think we need to require that MetadaSections in the Metadata element use 
in a PutMetadata contain an @Identifier. I propose we add the following 
sentence to the end of the first paragraph of the description of 
[Body]/mex:PutMetadata/mex:Metadata:
The mex:MetadataSections of this mex:Metadata element are REQUIRED to 
contain the @Identifier attribute (in addition to the mandatory @Dialect 
attribute).
~ gp