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10757Re: [soapbuilders] Multiple WS-Addresses in multiple namespaces

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  • noah_mendelsohn@us.ibm.com
    Feb 6, 2007
      Paul Downey writes:

      > I raised this very issue in my position paper [1] to the W3C Workshop
      > on Enterprise computing, and see it as a fundamental consequence
      > of SOAP not having a "stack", but a "bag" (actually a graph with WSS)
      > which requires meta-data such as the much trumpeted WS-Policy to
      > unravel.

      One of my great regrets about the SOAP Recommendation is that it does not
      make crystal clear an aspect of the design that I considered to be very
      important. Still, the crucial function is there IMO:

      First of all, it's not true that what SOAP has is a "bag"; the header
      elements are siblings in an envelope Infoset, and the Infoset is ordered.
      Also, headers may have interacting semantics [1] :

      "Mandatory SOAP header blocks are presumed to somehow modify the semantics
      of other SOAP header blocks or SOAP body elements."

      Furthermore, and this is crucial, while SOAP itself mandates no fixed
      order when processing, headers can be defined to control the order [1]:

      "The processing of one or more SOAP header blocks MAY control or determine
      the order of processing for other SOAP header blocks and/or the SOAP body.
      For example, one could create a SOAP header block to force processing of
      other SOAP header blocks in lexical order. In the absence of such a
      controlling SOAP header block, the order of header and body processing is
      at the discretion of the SOAP node. Header blocks MAY be processed in
      arbitrary order. Header block processing MAY precede, MAY be interleaved
      with, or MAY follow processing of the SOAP body. For example, processing
      of a "begin transaction" header block would typically precede body
      processing, a "logging" function might run concurrently with body
      processing and a "commit transaction" header block might be honored
      following completion of all other work."

      This is not an accident. It's why we require that all mustUnderstand
      checking be done before any other work. That's what ensures you that if
      you have an mU header that says "do the headers in reverse order" or
      "alphabetical order" or more likely "do signatures first" then that
      header or those headers will necessarily be checked in time to determine
      an order.

      Furthermore, and this is the part I really wish had been highlighted a bit
      more, nothing says these must be separate headers. So, IMO, if you want
      to say >in the specification for wsa:To< "if there are multiple wsa:To
      headers, here's the rule for how to process them all in the presence of
      the others", you can do so. If they are marked mU then you can be sure
      that, at least per the SOAP spec, their specifications can conspire to
      determine an order.

      In fact, what I really wanted to see in the recommendation would be a
      statement along the lines of: "The specifications for headers that may
      coexist in a SOAP message must collectively describe the correct
      interpretation of the headers in combination as well as in isolation.
      Thus, specifications may be written for families of headers designed to be
      used together, to determine operation in the case where multiple instances
      of the same header appear etc. Such specifications may call for a given
      header to be "understood" only when accompanied or only if not accompanied
      by certain other headers. etc."

      I think that is in fact implicit in what is there, but obviously many
      users have missed it. Whether the typical stacks out there provide much
      help in supporting such combined interpretation and ordering is a
      different question, but the spec definitely anticipates it IMO.

      Noah

      [1] http://www.w3.org/TR/soap12-part1/#muprocessing
      [2] http://www.w3.org/TR/soap12-part1/#procsoapmsgs
      --------------------------------------
      Noah Mendelsohn
      IBM Corporation
      One Rogers Street
      Cambridge, MA 02142
      1-617-693-4036
      --------------------------------------
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