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Subject: Re: [ws-caf] Nested contexts ( was RE: [ws-caf] Mt Everest and WS-CF)
Peter, I have a slightly different perspective that only sometimes involves transactions in the "shared outcome decision and distributed knowledge of that outcome" sense. When I think of linked contexts, I consider multiple activities that coincide with a particular message to form a nested stack of contexts applicable to that message. I guess nesting and interposition of transactions (with varying time spans I would assume) might be a derivative case. The (generic?) use case I am thinking of involves a message - sent securely (referring to an earlier authentication event), - within a transaction (lasting longer than the secure session in this case), - as part of an identified instance of a known choreography (effectively, two activities with the instance having a much shorter lifetime than the description of the choreography), - driven by SLA terms and other machine and / or humanly readable information about the larger contract between the enterprises involved (and legal documents are not small ;), - sent by / to / about a specific enterprise whose physical characteristics (shipping locations, for example) and other information is available to all parties, - et cetera (until the context describes the universe). The list above is not intended to be at all exhaustive or to imply that all messages require everything listed. It must remain an implementation or overall distributed application choice how much of the hierarchy gets mentioned (transitively in some cases) when sending a particular message. How I represent this stack of related contexts is probably an implementation choice at the moment. If I am correct (and using the old draft as a guide), the current specification makes no recommendations about how often to use the child pointers or whether multiple WS-Context headers should appear in the same message. Contexts with different lifetimes (including multiple contexts with varying senses of an infinite lifetime) could reasonably be all linked into one (nested, hierarchical, at least unified) list, could be sent as multiple WS-Context headers (one per context) or everything in between. Are you making a recommendation on way or the other or asking for this type of clarification in the documentation? Alternatively, are you suggesting that everything except nested or interposed transactions must be handled using separate WS-Context headers? Should mention that my leaning is toward a single WS-Context header per message. This might imply a receiver need understand only WS-Context and the semantics of the top level (outermost, shortest lived) context mentioned in that message. The WS-Context and dependent specification propagation rules should mean anything above the level they understand gets carried along for the ride. Does this align with your thinking? From what I have seen (and, no, I have not seen the soon-to-be-available-we-all-hope editors draft), WS-Context supports either type of linking (syntactic nesting or carrying in parallel with overlapping lifetimes) directly. The main issue seems to be clarifying the choices mentioned above so that all of the dependent specifications do not need to describe how they relate to every other context type. thanx, doug On 28-May-04 06:08, Furniss, Peter wrote: ... > The most-known use case for nested contexts is, I believe, the nesting > and interposition in transactions. Does that use really want to > propagate the entire ancestral (and colateral ?) tree ? Other > transaction protocols tend only to propagate the identifiers of the > immediate line. The present WS-Context nesting capabilities don't seem > to be well-aligned with that need. > > Peter
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