From: L.G. Meredith <lgreg.meredith@gmail.com>

Date: Tue, 20 Jun 2006 15:20:19 -0700

Message-ID: <5de3f5ca0606201520t4de5f2e0s27e0a8cbcd66ebd1@mail.gmail.com>

To: "Paul Bouche (HPI)" <paul.bouche@hpi.uni-potsdam.de>

Cc: public-ws-chor@w3.org

Date: Tue, 20 Jun 2006 15:20:19 -0700

Message-ID: <5de3f5ca0606201520t4de5f2e0s27e0a8cbcd66ebd1@mail.gmail.com>

To: "Paul Bouche (HPI)" <paul.bouche@hpi.uni-potsdam.de>

Cc: public-ws-chor@w3.org

Paul, Just to clariy my last point -- when i say 'latter activity' i mean the interpretation of gross, and not fine-grained, program structure. Best wishes, --greg On 6/20/06, L.G. Meredith <lgreg.meredith@gmail.com> wrote: > > Paul, > > Based on my cursory reading of your paper i would hazard that you have > gotten the evaluation criteria backwards. When a theory Y is claimed based > on a theory X, one must exhibit a map from Y to X, not from X to Y. Your > paper sought a mapping from \pi-calculus to WS-CDL. This is not what is > required to ascertain whether WS-CDL is based on the \pi-calculus. Rather, > one is looking for an interpretation (a map) of WS-CDL into the > \pi-calculus. In traditional programming language semantics symbols, you > seek something like a map > > [| - |] : WS-CDL -> \pi-calculus > > taking XML documents conforming to the WS-CDL schema and producing > expressions in the \pi-calculus. > > Now, several comments are in order. First of all, we know that this is -- > in principle -- possible. Why? Because the \pi-calculus is Turing complete. > Thus, unless WS-CDL offers a model of computation that is richer than Turing > machines -- highly unlikely -- we must be able to exhibit at least one such > map (in fact there are many). But, just because we can exhibit such a map in > no way actually justifies the claim "based on" the \pi-calculus. After all, > we can also exhibit an interpretation of WS-CDL in the \lambda-calculus and > finite automata with two pushdown stores and Turing machines and set theory > and first order predicate logic, etc. None of these maps justify any claim > of "based on". > > To justify this claim there must be some transparency of the mapping. > Something must be preserved in the translation. For example, the notion of > parallel composition maps directly to the notion of parallel composition, or > the notions of choice maps directly to the notion of choice, etc. In > symbols, you need something like > > [| <compose> WS-CDL-Process1 WS-CDL-Process2 <compose> |] = [| > WS-CDL-Process1 |] | [| WS-CDL-Process2 |] > > or whatever the tag is that represents parallel composition (or the notion > you seek to preserve). > > The more direct, i.e. transparent, i.e. the more that is preserved, the > more you find justification for the claim "based on". > > Secondly, note that the \pi-calculus, like the \lambda-calculus, is a very > impoverished model. It does not come with arithmetic types, or string types > or structured data structures. There are, needless to say, lots of ways to > interpret these notions as processes. But, that is unwieldy for practical > purposes like specifying business protocols. In the \lambda-calculus there > are very natural ways to embed these concepts at their standard levels of > abstraction. In the \pi-calculus this is a much more subtle game and i > submit that no one has found a particularly satisfying answer to this > particular problem. (There is the notion of applied \pi-calculus; and i have > investigated, more recently, notions of adding reflection to the > \pi-calculus, thus embuing names with the structure of processes.) > > With this in mind one may find that the interpretation preserves gross > program structure (parallel composition, sequencing, choice, etc); but not > fine-grained program structure (data types and conditionals expressed on > elements thereof). It is this latter activity that i believe the work on the > global calculus reflects, but, i have not kept abreast of it and could > easily be mistaken at this point. > > i hope this helps. > > Best wishes, > > --greg > > > On 6/20/06, Paul Bouche (HPI) <paul.bouche@hpi.uni-potsdam.de > wrote: > > > > Hi Gero, hi everyone else, > > > > in response to Gero's questions, I can partly answer the last I think > > because I have asked it here before. Here are three links I have found > > helpful in discovering more about the global calculus: > > [1] Carbone, Honda, Yoshida, "Programming interaction with Types" , > > http://www.w3.org/2002/ws/chor/5/06/F2FJune14.pdf > > > > [2] Kavantzas, "Aggregating Web Service: Choreography and WS-CDL", > > > > http://lists.w3.org/Archives/Public/www-archive/2004Aug/att-0017/WS-CDL-April2004.ppt > > > > > > [3] Honda, Yoshida, et. al. "A Theoretical Basis of > > Communication-Centred Concurrent Programming", > > > > http://lists.w3.org/Archives/Public/public-ws-chor/2005Nov/att-0015/part1_Nov25.pdf > > > > (I tried all of them just now so they should work fine). > > > > Concering the global calculus and the formal grounding work for WS-CDL > > the response I got was that more work on this is scheduled to finish for > > the end of October this year (?). > > > > Concering the relationship between Pi-Calculus and WS-CDL I have done > > some investigation in this as part of a seminar Gero also took part in. > > I have been thinking about for while now to just mail it to this list so > > as to contribute to the discussion and share my humble opinion on the > > subject; so I shall do it now as the opportunity arises. It at best > > might answer some of the questions Gero posed or at least might provided > > hints to answers. Find the paper attached and please comment as you > > wish. > > > > Have a great day! > > Paul > > > > Decker Gero wrote: > > > > >Hello everyone, > > > > > >I am currently working on my Master thesis (at SAP Research Brisbane) > > about service choreographies und therefore I am very interested in the > > activities of the CDL working group. > > > > > >I have a couple of questions regarding CDL: > > > > > >- It is claimed that CDL is based on pi-calculus which has proven to be > > extremely expressive. Sequence, parallelism, choice and message exchanges > > are enough to express common scenarios in the BPM domain. E.g. the > > workflow patterns and the service interaction patterns could be fully > > formalized. A trick in these formalizations is that each control flow > > construct is encoded using a set of processes that exchange messages for > > synchronization purposes. In CDL I do not see how I can do that. > > > > > >- Let us take a look at an example to clarify my question: Participant > > A receives a number of messages via channel b. After three messages have > > been received or a message has been received over channel c A continues by > > sending a message over channel d. In pi-calculus I could write: > > > A = (^h) (b(m1).b(m2).b(m3).'h.0 | c(m4).'h.0 | h.'d.0) > > >^h is a private name, b() a message receipt and 'h a message send. I > > introduced h to coordinate the two parallel processes. How does this work in > > CDL? In BPEL there is the notion of control links which seems quite > > powerful. > > > > > >- Another example would be (inspired by http://bpt.hpi.uni-potsdam.de/twiki/pub/Public/PiHypeExample/PiHypeExample.pdf > > ): there are seven interactions a, b, c, d, e, f, g, h. a must happen > > before b and e, b must happen before c, c must happen before d and f, d must > > happen before h, e must happen before f, f must happen before g and g must > > happen before h. Assuming a participant who is the sender in all these > > interactions and for each interaction there is a channel with the name of > > the interaction, the pi-calculus formalization for A would look as follows: > > > A = (^x1,x2,x3,x4,x5,x6) ('a.('x1.0|'x2.0) | x1.'b.'c.(' > > x3.0|'d.'x4.0) | x2.'e.'x5.0 | x3.x5.'f.'g.'x6.0 | x4.x6.'h.0) > > >How can I express this example in CDL? > > > > > >- How can I express scenarios where a participant A communicates with > > participants B1, B2, B3, ... which are all of the same role but only bound > > at runtime? E.g. like in the Single-transmission multilateral > > interaction patterns (http://sky.fit.qut.edu.au/~dumas/ServiceInteractionPatterns/Multilateral..html > > > > <http://sky.fit.qut.edu.au/%7Edumas/ServiceInteractionPatterns/Multilateral..html> > > ). > > > > > >- Concerning parallel interactions: Is it allowed that two interactions > > that do not have any preceding interactions happen in parallel? If so are > > there any restrictions concerning correlation information or which > > participant is involved in these initial interactions? > > > > > >- I read about some "global calculus". What is the current status? > > Although I like pi-calculus I am also very interested in a calculus that > > does not focus on interacting processes but rather communication from a > > global perspective. A similar expressiveness like pi-calculus would be > > desirable though. > > > > > >Best regards > > >Gero > > > > > > > > > > > > > > > > > > > > > -- > L.G. Meredith > Partner > Biosimilarity LLC > 505 N 72nd St > Seattle, WA 98103 > > +1 206.650.3740 > -- L.G. Meredith Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740Received on Tuesday, 20 June 2006 22:20:29 UTC

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