NEW ISSUE: (v1.2) Some way to "late bind" references to global domainchannels

Title: Some way to "late bind" references to global domain channels

    

    Target: Assembly 1.2 WD 03

    

    Description:

    

    Define some way that a composite can "late bind" references to
    global domain channels (GDCs) on the @targets of producers and
    @sources of consumers.

    

    Scenario A: A company that has multiple SCA domains - perhaps as a
    consequence of acquisition, or perhaps for testing and deployment
    purposes. However, they may want to deploy the same or similar SCA
    composites to each of those domains (as part of
    implementation.composite). However, for historical, management, or
    implementation reasons the GDCs have different names in the
    different environments. To reduce the amount of "wiring" of
    producers and consumers that needs to be done when actually
    deployed, it would be significantly easier to simply "late-bind"
    references to GDCs.

    

    Scenario B: A third-party developer of SCA composites defines two or
    more composites that can be deployed to an SCA eventing environment.
    To leverage eventing, said composites might most easily reference
    GDCs, such that when two or more of the composites from the
    third-party are deployed, they start communicating with each other
    as intended, and yet the manager of the domain can simultaneously
    guarantee that the requisite GDCs do not conflict with other uses
    already deployed.

    

    Proposal:

    

    (Note that this particular issue is a subset of the problems
    encompassed by ASSEMBLY-227, so a solution there could equally well
    apply here, but barring a solution to that which we can agree
    upon...)

    

    In the abstract:

    

    As per scenario B, the third-party developer is likely to want to
    refer to a well-known "subject/channel/topic" as developed by the
    third-party. In traditional naming scenarios, this is typically done
    with an XML QName, as in a WSDL portType, or an XML Schema
    ComplexType. To that end, the third party wants to define:

    
      
a logical QName, exposed as part of the componentType of a
        composite, that an assembler can bind to a particular GDC

      

      
a short-hand label that can reference the construct in the
        @source or @target attribute

      
a binding between that short-hand label and the logical QName.

    
    At least when it comes to #3, a logical choice for the short-hand
    label that makes #3 a no-op, is the "prefix:NCName" syntax common in
    XML.

    

    A composer, confronted with this extra thing in the componentType,
    needs a way to bind said QName to a particular channel.

    

    In referring to said logical reference, the @source or @target
    attribute can do something like:

    

    $tpns:global.channel.one

    

    (tpns - abbreviation for third-party name space)

    

    Since the "$" cannot be used in an NCName, this doesn't conflict
    with "private" channel references. Further, "/" is used to reference
    GDCs, so this syntax is not in conflict with that either.

    

    -Eric.