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Subject: RE: [ebxml-msg] Attributes specified in both the message and the CPA
David, Some comments below, as "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 ************************************************************************************* David Fischer <david@drummondgroup.com> on 11/01/2001 10:21:37 AM To: Dan Weinreb <dlw@exceloncorp.com>, ebxml-msg@lists.oasis-open.org cc: ebxml-cppa@lists.oasis-open.org Subject: RE: [ebxml-msg] Attributes specified in both the message and the CPA Hi Dan, I think you have made an assumption which is at the core of this problem. You have assumed that there is a pre-agreement. Many in this group agree with you but some don't. Take the case, for example, of someone requesting a stock quote. This may be a one-time transaction, and a rather simple one at that. Why go through all the trouble of negotiating a CPA? MWS: You still have to get both ends' middleware to agree on how to exchange the message. What you need is to be able to negotiate and deploy the CPA so rapidly that it can be thrown away after one use. Some people call it "dynamic eCommerce". Automated negotiation is a step in that direction. Take the case, for example, of someone purchasing a sweater from L.L.Bean. This is a B2C transaction and again, may be one time. Why bother with a CPA negotiation which takes longer than the transaction? MWS: My comment above applies. However let's face it. B2C works quite well today using browsers. What we are really after is dynamic B2B eCommerce. When we agreed not to require a CPA, we agreed not to require it. When we ask the question, "how does this work without a CPA?" we have to assume there is no CPA and no "virtual" CPA. Does this mean we have no configuration? Of course not, it only means there is no negotiation between the parties. MWS: Excuse me. You may call it "negotiation" or not but the two parties still have to understand each other's IT requirements or the message won't flow. What then is required in the message headers to accomplish this task? Many things, like persistDruation, retries, retryInterval, etc. can be given default or "bootstrap" values. MWS: Yes, you could throw the entire equivalent of the CPA into the message headers but you thus guarantee that two different implementations are required, one with and one without CPAs. Even the CPAId can be given a default -- like a credit card number -- or the sender can pick one and the receiver continues to use it. So we come down to -- what can't be given defaults? These are going to be transmission parameters such as syncReply, and parameters which may change per-message, like AckRequested. These are the things we need to maintain in both the MessageHeader and the CPA (my personal opinion is that syncReplyMode should be removed from CPA). MWS: OK, I think we more or less agree in these last two paragraphs. Someone else can comment on whether it makes implementation sense to dynamically change between sync and nonsync (or ack requested and no ack requested) for the same action. It makes perfect sense to define some actions as sync and others non-sync. Different messaging characteristics can be accounted for by defining different actions (i.e. different business transaction activities) in the BPSS spec. That's why the CPA provides for specifying a different delivery channel for each action. We also MUST allow ebXML-MS to work with a CPA -- which will probably be the most common case. To do this, we agreed NOT to override CPA values with values in the MessageHeader. Regards, David Fischer Drummond Group. -----Original Message----- From: Dan Weinreb [mailto:dlw@exceloncorp.com] Sent: Thursday, November 01, 2001 8:38 AM To: ebxml-msg@lists.oasis-open.org Cc: ebxml-cppa@lists.oasis-open.org Subject: [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 (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. 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. 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. (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. ---------------------------------------------------------------- To subscribe or unsubscribe from this elist use the subscription manager: <http://lists.oasis-open.org/ob/adm.pl> ---------------------------------------------------------------- To subscribe or unsubscribe from this elist use the subscription manager: <http://lists.oasis-open.org/ob/adm.pl>
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