- From: Sudhir Agarwal <agarwal@aifb.uni-karlsruhe.de>
- Date: Fri, 19 Sep 2003 17:10:52 +0200
- To: www-ws <www-ws@w3.org>
On Friday 19 September 2003 16:30, Bijan Parsia wrote: > An aside: I conclude from Drew's lack of response that I can declare > victory :) Congrats :-) Well, i think, Drew should define his Puzzle more clearly to avoid ambiguity in the interpretation of terminology. My questions to Drew: 1. What are C, P and Q? 2. What do you mean by a global and local time clock? In my opinion a global time clock is something different than a global process. Do you agree with that? 3. What do you mean by the entity that the first invocation of P creates? Regards Sudhir > > On Friday, September 19, 2003, at 02:38 AM, Sudhir Agarwal wrote: > [snip] > > >> Puzzle: Suppose C sends a message to P two or more times, at least on > >> some runs, e.g.: > >> > >> C = (seq (P) (if Q then ... else (P))) > >> > >> I've suppressed the actual dataflow, but assume that C is sending data > >> to P and getting some back. With respect to a run of C in which Q is > >> false after C interacts with (P), let P1 be that first interaction, > >> and P2 be the second. > >> > >> What exactly are P1 and P2? Is each a fresh invocation of the P > >> process? Is there a worldwide P process that everyone communicates > >> with (e.g., an atomic clock sitting in Geneva). Or does the > >> invocation P1 create an entity that C talks to when P2 occurs? How > >> are these different possibilities to be indicated? > > > > in my opinion, it depends on, who is controlling the execution of C. > > I disagree. It depends on 1) what services the process occurances > actually get instantiated to, and 2) how the service provider > implements the advertized semantics. > > Someone, somewhere, has to care about 1. Someone, sometimes, other than > the provider, might care about 2 but it may typically be the case that > she can't know anything and needn't be bothered by the fact. > > I am, of course, assuming that the semantics of these various > alternative Drew puts forth all respect the semantics of the > description under which P was selected. Indeed, if P was abstract, I > can see P's occurences being bound to services from *two different > providers*. > > > In case > > the execution of C is centrally controlled, for example by the > > provider of C, > > then one can assume a global clock (clock of C's provider). > > Seems like a wildly faulty assumption to me? Unless you mean that it > doesn't matter which way you assume? > > > If the execution > > is distributed, that is each participant (provider of component > > services) > > executes "his" part of the run independently of other participants, > > then one > > should assume each participant having a local clock and no global > > clock. > > Huh? They could all use the same clock. Why couldn't they? > > > In > > this case, each participant works sequentially (total order), whereas > > the > > whole run is executed concurrently (partial order). > > > > Spontaneously i would say that each invocation of P is a different > > instantiation. > > [snip] > > From the composite process POV, there's certianly some sense in which > we regard it as such (different process occurances). But I don't see > why we have to percolate this down. > > Take a simpler example. I do a series of GETs on an URI. I have NO CLUE > whether I'm getting a single web server, something out of a farm, > something from an intermediate cache or proxy. Nor do I care. Nor > should I, in most cases. > > I certianly can *build* some of these distinctions in, perhaps, but the > possibility of don't know, don't care needs to be preserved, and is > probably the default. > > So this is how I understand the Service Oriented Architecture model. > > Cheers, > Bijan Parsia.
Received on Friday, 19 September 2003 11:12:28 UTC