Dominic, Sorry, I missed a step so I withdraw one of my questions below... On Aug 28 2007, parkinm@cs.man.ac.uk wrote:
On Aug 27 2007, Dominic Battre wrote:
Thank you very much, Karl, for giving a lot of insight what is behind WS-Agreement.
Furthermore, 2PC can be synthesized with two WS-Agreement round-trips and an appropriate domain-specific agreement semantics. So, either advance reservation, combined with the right cost/penalty model, or the underlying invitation system can both look like 2PC in practice:
I tried to digest that and this is what I came up with:
https://cit-server.cit.tu-berlin.de/trac/negmgr/wiki/TwoPhaseCommit
Between step 5 and 6 of this protocol, how long does the provier wait for a response? As there is no facility for the user reject an offer in this protocol and let the provider know it doesn't want the advance reservation - the provider must specify a time limit to the offer, no? As was said in an earlier email - you can't assume agreement is going to happen...
Sorry, please ignore this comment - I just saw the "User can cancel advance reservation offer for cheap fee" step.
Also, what happens if between step 5 and 6 another user wants to reserve the same resources? What does the provider do then?
As I mentioned in a previous email, the provider cannot offer those resources to the second user because if the first user accepts and the second user acccepts too, there is a problem of overcommitment of resources.
(I used my wiki because it supports tables)
It would be great, if you could have a brief look at it and tell me whether this is what you had in mind.
If some people want to contribute, I'd be interested in starting to write a "Best Practices in WS-Agreement" / "Design Patterns in WS-Agreement" / "WS-Agreement cookbook" / ... document.
Yes, I am interested.
This issue of 2PC for example would be a good candidate for such a document. I think it would really help if we find a place to collect examples, approaches of modeling something, approaches of implementing something, ...
I could easily contribute lots of questions but maybe some answers as well.
Thanks,
Michael.