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Subject: Re: [ebxml-cppa] [ebxml-msg] Attributes specified in both the messageand the CPA
David, some comments below, labelled MWS: Regards, Marty ************************************************************************************* Martin W. Sachs IBM T. J. Watson Research Center P. O. B. 704 Yorktown Hts, NY 10598 914-784-7287; IBM tie line 863-7287 Notes address: Martin W Sachs/Watson/IBM Internet address: mwsachs @ us.ibm.com ************************************************************************************* Dan Weinreb <dlw@exceloncorp.com> on 11/01/2001 09:37:42 AM Please respond to Dan Weinreb <dlw@exceloncorp.com> To: ebxml-msg@lists.oasis-open.org cc: ebxml-cppa@lists.oasis-open.org Subject: [ebxml-cppa] [ebxml-msg] Attributes specified in both the message and the CPA In a recent ebXML MS phone meeting, we talked about how to deal with attributes and properties of messages that appear to be specified both in the CPA and in the message itself. I said that I would try to put together a list of these. I assume that every ebXML MS conversation is governed by a pre-agreement on parameters, whether specified in an actual CPA document or by some other means ("virtual CPA"). If values are pre-agreed then why bother to reiterate them in the message itself? We discussed two possible answers: (1) to let the sender control the attribute on a per-message basis, and MWS: Any parameter that can be varied on a message by message basis doesn't belong in the CPA. The problem is if there are any parameters that are USUALLY static but might occasionally want to be varied per message. We would need to identify such parameters and agree that they need to be able to be varied. Those parameters might require indicators in the in the CPA. The cleanest way to do that would be to add a Boolean "variable" attribute on those parameters in which if set to "variable", the message would, for that CPA, always override what might be in the CPA. At this point I don't know of any CPA fields that might sometimes have to be varied per message. (2) so that intermediaries, who may not be privy to the pre-agreement, can see the values. If, for some attribute, neither of these is a concern, then there would not seem to be any reason for the attribute to be reiterated in the message. MWS: This is part of the whole issue of what functions intermediaries perform. One obvious exception: the message header should contain whatever fields are necessary to identify the message, especially whatever is necessary to establish which pre-agreeement applies to the message. Thus there's nothing wrong with MessageHeader subelements From, To, CPAId, ConversationId, Service, Action, and MessageId. Here is a list of thing that *might* constitute attributes that are specified in both the CPA and the message. In cases where I'm not sure, I err on the side of inclusion. Section 7.4 says "This parameter information can be specified in the CPA or in the MessageHeader", but some of the parameters listed among the subsections of 7.4 do not appear to be in the MessageHeader, or indeed in the message at all: Retries, RetryInterval, PersistDuration. Perhaps the wording in section 7.4 proper needs a small change. MWS: The wording in section 7.4 needs a BIG change. I believe this is already in the issues list. For each of the subsections of 7.4, it has to state whether the parameter is in the CPA or in the message header. In other words, this is not a designer's choice. Ver. 1.0 simply inadvertently omitted this information. Taking all this into account, there actually don't seem to be very many conflicts. The ones I can see that deserve scrutiny are: (1) syncReply The message has MessageHeader/QualifyOfServiceInfo/@syncReply (3.1.7.1) with values true and false. The CPA has CPA/PartyInfo/DeliveryChannel/Characteristics/@syncReplyMode (7.5.11.1) with values "signalsOnly", "resonseOnly", "signalsAndResponse", and "none". The CPA certainly appears to be talking about BPSS "signals" and BPSS "Business-response Messages", whereas the message header seems to be talking about MS-level acknowledgement. There has been a lot of discussion of this one already and I won't attempt to recap it here. (2) duplicateElimination / idempotency The message has attribute MessageHeader/QualifyOfServiceInfo/@duplicateElimination (3.1.7.2) with values true or false, while the CPA has attribute CPA/PartyInfo/DocExchange/ebXMLBinding/ReliableMessaging/@idempotency (7.6.4.2) with values true or false. These really do seem to mean the same thing. MWS: For version 1.0 they do mean the same thing. For version 1.0, it was asked why idempotency needs to be in the CPA at all since use of reliable messaging includes idempotency test (duplicate elimination). For version 1.1, the F2F ended up breaking out 6 or 8 separate Boolean parameters that together define the delivery semantics. The CPA will have to agre with however this redefinition comes out in the MS spec. This point applies to all the following paragraphs. (3) request for acknowledgement / deliverySemantics The message has DeliveryReceiptRequested (6.1.1) with "signed" attribute that can be either true or false, and AckRequested (7.3.1) with the same "signed" attribute and an "actor" attribute. The CPA has the attribute CPA/PartyInfo/DocExchange/ebXMLBinding/ReliableMessaging/@deliverySemantics with possible values "OnceAndOnlyOnce" and "BestEffort". These do not mean exactly the same things, but they seem to at least overlap. The CPA "deliverySemantics" attribute has only two possible values, rather than expressing all four possibilities the way the Message Specification currently does. The four possibilities are: Name Retry/ack? Dup elimination? BestEffort No No AtLeastOnce Yes No AtMostOnce No Yes OnceAndOnlyOnce Yes Yes In fact, it seems to me that it's not altogether clear what would be meant by setting deliverySemantics to OnceAndOnlyOnce and setting idempotency to true. If you know that a message is idempotent then "only once" is not important, and effort spent preventing duplicates may not be worth the cost. MWS: I think there is a problem with interpreting the word "idempotent". Formally, idempotent means that repeating the function will produce the same result and therefore it is not necessary to eliminate duplicates, which I think is what you are saying here. The problem (which I think we discussed at the F2F) is that "idempotency" in our context means "test for duplicates" (a common misuse of the word "idempotency"). We should say "eliminate duplicates", not "idempotency". MWS: I agree: The problem with splitting delivery semantics into a bunch of boolean parameters means that some combinations are meaningless and in other cases, settings of two different parameters to "yes" is a redundancy. ---------------------------------------------------------------- To subscribe or unsubscribe from this elist use the subscription manager: <http://lists.oasis-open.org/ob/adm.pl>
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