Interpretation of PMode.ID

Hello,

    

    Here is a question from an AS4 implementer:

    

      
According to [CORE] Appendix D 3.1 "[The PMode ID] may
            be absent if the P-Mode is identified by other means, e.g.
            embedded in a larger structure that is itself identified,
          or has parameter values distinct from other P-Modes used on
          the same MSH. If the ID is specified, the AgreementRef/@pmode
          attribute value is also expected to be set in associated
          messages."

      
      
      
[AS4] 2.2.3.1 makes support for
          PMode.ID required. How does that work
          with the situation above where the PMode is embeded in a
          larger structure? What does a MSH have to do to support
          Pmode.ID? 

       

    

    This "ID" feature seems somewhat underspecified and therefore
    subject to interpretation/implementation or profiling. Basically, a
    PMode determines the configuration to use for outgoing messages and
    to use --and validate-- for incoming messages. If PModes have IDs,
    then the receiver MSH does not have to infer the configuration (e.g.
    from other header values, as described in "example 1" in section
    D.1) but can do a direct lookup (as described for "example 2"). 

    

    My interpretation (from the spec and discussions) is that, "support
    by an MSH" means that the MSH can have PModes with an ID, and if a
    PMode has an "ID", the "support by an MSH" means that the sending
    MSH MUST include it with outgoing messages, and a receiving MSH MUST
    use it to retrieve a specific configuration. So the required support
    in AS4 would requires the ability to attach an identifier to a
    PMode.

    

    1) Do you agree with this interpretation?

    

    2)  If a sender does not include an ID in a message,  should the
    receiving MSH match it against PModes that do not have an ID only, 
    or to all PModes (some that have, and some that do not have a PMode
    ID) ?   

    

    3)  If a sender includes an ID in a message, and the receiving MSH
    does not have a PMode with this ID,  should it return an error or
    should it attempt to match the message to PModes without ID (i.e.
    ignore the ID)

    

    Kind Regards,

    

    Pim