From: Gary Brown <gary@pi4tech.com>

Date: Thu, 03 Aug 2006 09:12:57 +0100

Message-ID: <44D1B009.9010206@pi4tech.com>

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

CC: Kohei Honda <kohei@dcs.qmul.ac.uk>, Marco Carbone <carbonem@dcs.qmul.ac.uk>, Steve Ross-Talbot <steve@pi4tech.com>, WS-Choreography List <public-ws-chor@w3.org>

Date: Thu, 03 Aug 2006 09:12:57 +0100

Message-ID: <44D1B009.9010206@pi4tech.com>

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

CC: Kohei Honda <kohei@dcs.qmul.ac.uk>, Marco Carbone <carbonem@dcs.qmul.ac.uk>, Steve Ross-Talbot <steve@pi4tech.com>, WS-Choreography List <public-ws-chor@w3.org>

Hi Greg Just to respond to your last point, I think there is definitely a place for both 'full blown choreographies' representing a global view of a set of interacting services, as well as a description of the specific behavior associated with a service. They have different roles to play. The global model provides a design approach to enable the responsibilities of each service to be understood with respect to a particular business process. This global model can then be used to derive the behavior of a new service, or ensure that existing legacy services conform to the required behavior (using the service's observable behavior description). Similarly, as you have described, if a service has its own endpoint behavior description, then it would be possible to do a behavioral equivalence lookup within a service registry. However, the required service behavior could be derived from the choreography. At the moment Marco and Kohei's type system addresses both of these aspects, it is only WS-CDL that is lacking an endpoint representation - which as you have pointed out would ideally be a simple extension to WSDL. But that was not within the charter of the working group. However, this is one area where potentially abstract BPEL may provide a solution, but that does not preclude other more compact notations being associated with the WSDL in the future. Regards Gary L.G. Meredith wrote: > Kohei, > > Many thanks for the edifying remarks. i hope you will allow me to > probe on a related front. > > Suppose we took a different approach to the architecture of WS-CDL in > which what is published is something like (collections of) Kobayashi's > usages, (an appropriately XML-ified version of) which could be seen as > a simple and direct extension of WSDL, leaving more detailed > descriptions of service logic (in which resides potentially > proprietary business value) behind the firewall, so to speak. > > i emphasize publish in this context because i want to call attention > to what's of general public interest in a service description. i argue > that the primary function of a public service description is search. i > submit that in a world where SOA is the norm there will be billions of > services, and a service consumer will need to find services that > > * do what they need them to do (a semantic question) > * do it in a way that is compatible with their own needs and > practices > > Further, i argue that the former is far more important than the > latter. Consider the case where there is only one provider. The > consumer will adapt to any incompatibility. (Note that just because > there is only one such provider does not alleviate the search burden. > The consumer may not know of the provider, even when there is only one.) > > i want to argue that a great deal of semantic information can be > gleaned from information about behavior. i can provide some > interesting and illustrative examples, if you want them. One question, > however, is how much information needs to public to help the consumer > address their needs, and what needs to remain behind the firewall to > protect hard won business value? > > Now, to bring this line of reasoning back to my question above. Does > the market need a standard to capture full-blown choreographies? Or, > is there another niche that is likely to see better adoption? For > example, consider a small extension to WSDL, like Kobayashi's usages, > which can -- in Marco's words more powerfully and more generally -- > ensure both compatibility issues (like eliminating deadlock) and > increase the information available by which to conduct semantic-based > search one. > > Best wishes, > > --greg > > On 8/2/06, *Kohei Honda* <kohei@dcs.qmul.ac.uk > <mailto:kohei@dcs.qmul.ac.uk>> wrote: > > Hi Greg, > > It is great to get reactions so quickly. > > L.G. Meredith wrote: > > Marco, Kohei, > > > > Thanks for clarifying. i was refering to the EPP theorem on page 85, > > which i took as the central result of the work. Sorry, if i was > a bit > > eliptical. My thought was that the end point calculus is actually a > > type system and end point projection was like the calculation of a > > kind of minimal type. Then, you can see the EPP theorem in the > light > > of subject reduction. > > I may rather say that the global calculus and the end point > calculus are > two different description > languages, each with its own typing system, with respective notions of > minimum typing. > > The type structures are common, but the way descriptions are typed are > quite different. > > The idea is to project each "well-formd" global description to a > collection of endpoint processes, > which are the code for the participants involved. > > What the EPP theorem asks is: > > Do these projected participants interact following a scenario > (choreography) which the > original global description has laid out? > > It turns out that, if a global description satisfies certain > well-structuredness, or "healthiness conditions", > then > > (1) there is a very simple endpoint projection, and > (2) the correspondence in behaviour is as exact as can be. > > There are three well-structuredness conditions we have identified. We > believe they offer a natural > way to do a well-structured global description. > > I will post a brief discussion on the engineering meaning of this > result, but for the time being let us > say the EPP theorem offers a way to relate the global description > languages and the process calculi. > The latter gives rigorous theories of behaviours, their properties > and > composition, while the former > offers a useful engineering medium. > > > > i know that you have a separate notion of typing laid out in the > > paper, but i tend to think -- much in the way Kohei laid out -- of > > towers of typing of increasing strength. Abramsky gives a good > example > > of such in his Marktoberdorff lecture with Simon Gay and Raja > > Nagaranjan on types for concurrency. > > On this point I firmly agree: types and various analyses including > process/program logics are great toos > especially when we know how to integrate them consistently. > > > > > > That said, i was trying to draw an analogy between the EPP and > > Kobayashi's usages. More specifically, in my mind there is > connection > > between the fact that EPP is a function and Kobayashi has a type > > inference algorithm -- apart from the practical implication that the > > programmer doesn't have to write the type. > > So the EPP theorem is not so much about type discipline or program > analysis but rather about a basic way > to relate two distinct ways of describing interactions. It is like the > result on encoding of some calculi into > the pi-calculus, saying the encoding fully respects the original > dynamics, under certain conditions. > > These "under certain conditions" are the well-structuredness > (healthiness) conditions. > > I will discuss on the general picture further in my coming post. > > Best wishes, > > kohei > > > > > > > Best wishes, > > > > --greg > > > > On 8/2/06, *Marco Carbone* <carbonem@dcs.qmul.ac.uk > <mailto:carbonem@dcs.qmul.ac.uk> > > <mailto: carbonem@dcs.qmul.ac.uk > <mailto:carbonem@dcs.qmul.ac.uk>>> wrote: > > > >> This looks like a lot of work. i may be misreading, because i > >> have only skimmed, but it looks as though the main theorem > is a > >> subject reduction-like theorem in which the subject > reduction is > >> simulation-style (ala Kobayashi's type systems) as opposed to a > >> static subject reduction (ala Honda, et al's type systems). > Have > >> you seen, therefore, Kobayashi's 2006 types for concurrency > paper ( > > > > > > Just to clarify, the paper has three main theorems: > > > > 1) Subject Reduction for the global calculus type system > (session > > types) i.e. when the system evolves it is still well typed ( > e.g. > > I evolves to I' and I is well typed then also I' is well typed. > > > > 2) Subject Reduction for the end-point calculus (similar to > point 1) > > > > 3) EPP Theorem, i.e. > > a) Type Preservation i.e. a well typed global description is > > projected to a well typed global interaction. > > b) Completeness i.e. if a global interaction I evolves to I' > then > > its projection evolves to the "projection" of I' (EPP(I') ) > > c) Soundness i.e. if a projection EPP ( I ) evolves to N then I > > can evolve to I' and the projection of I' is "similar" to N > > > > 1) and 2) guarantee that working with typed programs is safe > (you > > never evolve to untyped i.e. unwanted things). > > > > 3) shows that given a global description (e.g. a WS-CDL > > choreography), its end-point projection is good and respects > what > > the programmer wanted to specify in the choreography. > > > > Hope this clarifies the key points of the paper. > > > > Best, > > Marco > > > > P.S. > > I didn't read the paper you linked but I believe it is related > > with another of his works i.e. having CCS processes as types. > > Session types are related to this but Kobayashi's are much more > > powerful and lose. > > > > > > > > > >> > http://www.kb.ecei.tohoku.ac.jp/~koba/papers/concur2006-full.pdf > <http://www.kb.ecei.tohoku.ac.jp/%7Ekoba/papers/concur2006-full.pdf> > >> > <http://www.kb.ecei.tohoku.ac.jp/%7Ekoba/papers/concur2006-full.pdf>)? > >> > >> Best wishes, > >> > >> --greg > >> > >> On 8/1/06, *Steve Ross-Talbot* < steve@pi4tech.com > <mailto:steve@pi4tech.com> > >> <mailto:steve@pi4tech.com <mailto:steve@pi4tech.com>>> wrote: > >> > >> > >> Is at: > >> > >> > http://lists.w3.org/Archives/Public/www-archive/2006Aug/att-0000/ > <http://lists.w3.org/Archives/Public/www-archive/2006Aug/att-0000/> > >> workingNote.pdf > >> > >> Please read and comment as soon as possible. > >> > >> Cheers > >> > >> Steve T > >> > >> > >> > >> > >> -- > >> L.G. Meredith > >> Partner > >> Biosimilarity LLC > >> 505 N 72nd St > >> Seattle, WA 98103 > >> > >> +1 206.650.3740 > > > > --------------------------------------------------------- > > Marco Carbone > > > > Dept. of Computer Science > > Queen Mary University of London > > Mile End Road > > E1 4NS London > > United Kingdom > > > > Phone: +44 (0) 207 882 3659 > > Fax: +44 (0) 208 980 6533 > > email: carbonem@dcs.qmul.ac.uk > <mailto:carbonem@dcs.qmul.ac.uk> <mailto:carbonem@dcs.qmul.ac.uk > <mailto:carbonem@dcs.qmul.ac.uk>> > > home: http://www.dcs.qmul.ac.uk/~carbonem > <http://www.dcs.qmul.ac.uk/%7Ecarbonem> > > < http://www.dcs.qmul.ac.uk/%7Ecarbonem> > > --------------------------------------------------------- > > > > > > > > > > -- > > 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 Thursday, 3 August 2006 08:13:30 UTC

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