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*2.4.7. Choreography Life-line, the eighth para. The operational behaviour involving "complete condition" is not clear. Is the condition evaluated lock-step, at each action? It at least needs transaction semantics for all related variables. Suppose a variable V should have the value [not W]. Suppose W should have the value [not V]. We never know it is true or not, especially if they are situated in different roles. As a possible way to record this point, one may augment the 3rd sentence as: "A complete condition MUST be possible to be matched in all Roles that participate in the Choreography, for which we assume a consistent global view is maintained." This is a very useful feature, I can see, but I feel like recording a bit of subtlety inside the spec.
agreed on con call 15-feb-05: requires clarification from issue raiser (Kohei Honda). Action on Gary to followup
Clarification from Kohei Honda: http://lists.w3.org/Archives/Public/public-ws-chor/2005Mar/0042.html I wrote: > The operational behaviour involving "complete condition" is not clear. > Is the condition evaluated lock-step, at each action? It at least > needs transaction semantics for all related variables. This is based on a literal reading of the draft (which is what the public would do). In the choreography element, we specify "complete" condition. This is not shared by multiple roles but are local to each of them. Hence I wonder how we know all these different complete conditions are matched. I believe the only possible way is (1) For each role to evaluate it each time as computation proceeds; (2) If it evaluates to true it would pause a bit, asks a coordinator (of some sort, should be provided by infrastructure) about the global situation; (3) If everybody agrees it is the time to complete well let's complete. We need two-phrase commit or some sort to make this precise, but this is technical (and anyway as far as it conforms to 1.6, timing assumptions, it should be OK). There are two further notes: * If this is what is expected, we should put some such bits (that we assume "all should agree that it is the time to complete" so that the expected behaviour is clear. My proposal, slightly changing what I wrote, is: "A complete condition MUST be possible to be matched in all Roles that participate in the Choreography, for which we assume an appropriate idea of synchronisation." I am not satisfied with this, but some such line would be necessary. * Adding operational bits is not going to execution logic, we need to specify behaviours consistently and clearly. So it does not violate e.g. 1.5. I will write soon about the next issu, Issue 1107. I hope these will be ready for today's conf call. kohei
Further clarification from Kohei Honda: http://lists.w3.org/Archives/Public/public-ws-chor/2005Mar/0045.html A tiny refinement of my phrasing. What I wrote: > > "A complete condition MUST be possible to be matched in all Roles that > participate in the Choreography, for which we assume an appropriate > idea of synchronisation." > may better be: "A complete condition MUST be possible to be matched in all Roles that participate in the Choreography, for which we assume that consistent, unanimous agreement among the Roles can be reached on the current state of the complete condition by the help of, for example, an appropriate synchronisation protocol." Note by saying "unanimous agreement" we assume each process is working all right, even if there are exceptional circumstances: if some process ceases to work or goes crazy, then we cannot use this mechanism, we need e.g. voting, but this detail may not be suitable for CDL description. I note this for drawing attention to possible scenarios the idea described above can cope with. kohei
at June 2005 F2Fwe agreed to close wontfix: http://lists.w3.org/Archives/Member/member-ws-chor/2005Jun/att- 0003/June_2005_F2F_minutes_-_0.txt
group notification of status change: http://lists.w3.org/Archives/Member/member- ws-chor/2005Jul/0004.html
no comments from group so closed confirmed: http://lists.w3.org/Archives/Member/member-ws-chor/2005Jul/0004.html