RE: TIP - node rules
Peter Furniss <p.furniss@ulcc.ac.uk> Fri, 08 August 1997 12:30 UTC
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From: Peter Furniss <p.furniss@ulcc.ac.uk>
To: 'Tom Freund' <tjfreund@uk.ibm.com>
Cc: tip <tip@tandem.com>
Subject: RE: TIP - node rules
Date: Fri, 08 Aug 1997 12:55:52 +0100
Encoding: 73 TEXT
Tom, > > One kind of rule, essential because of the two-pipe mechanism, is making > > sure the top-node (the travel agent in the requirements example) does not > > initiate commitment until all the subordinates have registered. > > Generalising this precisely may not be that easy. A particular might be: > > Doesn't the general rule need to also state that all applications > messages must have been > received by a server ... this would be the equivalent of the > OTS/implicit/checked behavior? Yes, there has to be a rule corresponding to the one I gave to say "don't initiate commitment until all the replies are in, and yes this is the same as OTS (or X/Open) checked behaviour. (and the need for it in those shows that they are semanticaly two-pipe, by the way) But the general rule appropriate to the TIP specification (as opposed to TIP + P spec) ought to permit cases beyond the request/response paradigm. A spec that allowed: [ P(stuff) means "stuff" is sent as fields of an application message ] A->B: P(start negotiation, TIP URL (at TM A)) TM B -> TM A: PULL TM A -> TM B: PULLED B->A : P (started, price list) A->B : P( buy N of item X as quoted) Ap A requests TM to initiate commitment TM A-> TM B: PREPARE is safe, because Ap B won't let TM B allow the commitment (and thus send PREPARED) until and unless it has purchase secured. There may be another application message from B->A, but that could come after the whole commitment exchange is over. I know that is not a client-server example ( Ap B can't be run as simple server that exits with ok/not-ok before the commitment starts), but the TIP protocol at present would allow it, and I don't think we would want to *forbid* it in stating guidance rules for TIP + P specs. Or would we ? > Another case, not specifically on this point but related is > out-of-sequence messages ... i.e. a failure > in the server causes the server to restart at some random point in the > application message flow (btw a > point which is not covered in the OMG/OTS specification). (I assume "server" here means the top transactional node, not the leaf server) A server that isn't sure where it is in the transaction surely ought not request/allow commitment. Otherwise, there is a general problem of being sure both sides agree on what they are committing to. I think this is probably a TIP + P matter, though it links to the security issue (especially the non-repudiation needed for e-commerce). A problem I can see is that can be different application protocols on the branches (as in the requirements example - the airline and hotel booking may use different protocols, or at least different URL-in-HTTP specs). Using the undefined space at the end of TIP statement, as Keith suggested, sounds like a good approach. Peter Peter Furniss Consultants 58 Alexandra Crescent, Bromley, Kent BR1 4EX, UK Phone & fax : +44 (0)181 313 1833 (or 0181 460 8553 if busy) Email : P.Furniss@ulcc.ac.uk
- Re: TIP - node rules Tom Freund
- FW: TIP - node rules Lele, Vishwas
- RE: TIP - node rules Peter Furniss