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Subject: RE: [soa-rm] Opacity calumny
> For example, if I take an existing client-server system and > just advertise the interface to that server - does this give > me SOA? IMHO, no. The reason is that with client-server, a client is a client and a server is a server. With SOA, a service may act in both capacities (consumer and producer - or whatever terms you would like to use). Joe Joseph Chiusano Booz Allen Hamilton O: 703-902-6923 C: 202-251-0731 Visit us online@ http://www.boozallen.com > -----Original Message----- > From: Bashioum,Christopher D [mailto:CBASHIOUM@mitre.org] > Sent: Wednesday, July 13, 2005 9:47 AM > To: Chiusano Joseph; soa-rm@lists.oasis-open.org > Subject: RE: [soa-rm] Opacity calumny > > I agree with your assertion of a continuum that goes from > uncoupled to tightly coupled. However, I am not so sure that > the concept of loose coupling does not belong in the RM (but > not convinced it does, either). > > > For example, if I take an existing client-server system and > just advertise the interface to that server - does this give > me SOA? What if the client and the server are very tightly > coupled - where the client sometimes sends messages to the > server and sometimes just directly accesses the data store > that the server is using? What if the client and the server > both share the data store, and only send messages to each > other when the data store is updated? > > I am still struggling with this, as I am not sure how to > "measure" the degree of coupling, and even if I did know how > to measure it, I am not sure what the threshold would be for > SOA. But, just because it is hard, I would hate to not > address it. I think that the idea of loose coupling (however > subjective that is) is inherent to SOA. If you don't have > it, you don't have SOA. > > Thoughts? > > -----Original Message----- > From: Chiusano Joseph [mailto:chiusano_joseph@bah.com] > Sent: Wednesday, July 13, 2005 9:32 AM > To: soa-rm@lists.oasis-open.org > Subject: RE: [soa-rm] Opacity calumny > > I believe that the degree of coupling is something outside > the scope of an RM, as it is more of a concrete aspect. It > does, however, belong in an RA and within concrete domain > architectures. > > Joe (not Duane hijacking Joe's e-mail account;) > > Kind Regards, > Joseph Chiusano > Booz Allen Hamilton > O: 703-902-6923 > C: 202-251-0731 > Visit us online@ http://www.boozallen.com > > > > -----Original Message----- > > From: Bashioum,Christopher D [mailto:CBASHIOUM@mitre.org] > > Sent: Wednesday, July 13, 2005 9:14 AM > > To: Michael Stiefel; soa-rm@lists.oasis-open.org > > Subject: RE: [soa-rm] Opacity calumny > > > > Agreed - so is there something about the loose coupling and > the design > > of the interfaces that is peculiarly SOA (and thus would fit in the > > RM), or is a tightly coupled interface still ok? I tend to > think that > > we need to capture something in the RM that focuses on > loose coupling > > - which is similar to the OO concept of public vs. private (Frank's > > earlier assertions). > > > > -----Original Message----- > > From: Michael Stiefel [mailto:development@reliablesoftware.com] > > Sent: Wednesday, July 13, 2005 9:01 AM > > To: Bashioum,Christopher D; soa-rm@lists.oasis-open.org > > Subject: RE: [soa-rm] Opacity calumny > > > > I agree. > > > > Access through interface does not, however, automatically get you > > loose coupling. Poorly designed interfaces can produce > tight coupling. > > > > Michael > > > > At 09:37 PM 7/12/2005, Bashioum,Christopher D wrote: > > > Ken, et. Al., > > > > > >I was reading your email thread and started thinking about > opacity as > > it > > >relates to the concept of loose coupling. It seems to me > > that the real > > >issue is loose coupling as opposed to opacity per se. One could > > publish > > >all the specs related to a service, including the actual > > code, as part > > >of the service description. As long as access to the > > internals of the > > >service is strictly via the interface, then you still have loose > > >coupling (and, a service). If, on the other hand, you don't tell > > anyone > > >about the internals of a service, but you still allow > access to the > > >internals via globals or back-door methods, you will not > have loose > > >coupling. > > > > > >I think opacity is really a surrogate for loose coupling. > In other > > >words, its not about what you know of the service via its > > metadata, its > > >what you can access of the internals of the service (thus the > > >private/public that Frank mentions). Ken - I think this is > > also what > > >you were trying to say also (thus, the ever more violent > agreements > > >below). So, that being said, we should probably address this more > > >succinctly in the document. > > > > > >-----Original Message----- > > >From: Ken Laskey [mailto:klaskey@mitre.org] > > >Sent: Monday, July 11, 2005 5:24 PM > > >To: Michael Stiefel; Frank McCabe > > >Cc: soa-rm@lists.oasis-open.org > > >Subject: Re: [soa-rm] Opacity calumny > > > > > >Agree, agree, agree. This list is getting much too tame. > > > > > >I would suggest that the concept of opacity is relevant to > > the RM, and > > >the fact that there are tradeoffs and examples of tradeoffs > > is relevant > > >to the RM. I also think relating this to a/c/p is relevant > > to the RM. > > >Being an engineer, it is difficult to list all the > problems and not > > >propose solutions, but alas that is not part of the RM. > So what of > > >this is appropriate for the RA? > > > > > >Ken > > > > > >At 05:09 PM 7/11/2005, Michael Stiefel wrote: > > > >I agree as well. > > > > > > > >Opacity is a design tradeoff and hence a concrete, not abstract > > issue. > > >All > > > >other things being equal more opacity is better than less, but in > > >reality > > > >you are trading off opacity for other things such as how much > > metadata > > >you > > > >publish and how much dependency you generate as a result. > > > > > > > >Michael > > > > > > > >At 04:31 PM 7/11/2005, Ken Laskey wrote: > > > >>Frank, > > > >> > > > >>To agree even more violently, this raises (and I allude > > to a little > > in > > > > > > >>the draft) the question of how to provide a means to publish > > metadata > > >as > > > >>it is found to be needed but in a way that supports a > > consistent use > > >of > > > >>the metadata in evaluating an entity against > unambiguously stated > > >a/c/p, > > > >>which themselves can be augmented and will evolve to > meet business > > >needs > > > >>of the users (where if I am a design engineer, my > business need is > > to > > > >>find the technically correct solution engine). > > > >> > > > >>This represents a much ignored need as well as a > terrible run-on > > > >>sentence. :-) > > > >> > > > >>Ken > > > >> > > > >>At 04:10 PM 7/11/2005, Frank McCabe wrote: > > > >>>Ken: > > > >>> > > > >>> I think we are in violent agreement. The essence of > the Java > > > >>>execution engine example is that it is precisely that the > > > >>>implementation is important -- not whether or not its > > good style!! > > > >>> > > > >>> Incidentally, if it is important to know who wrote the > > > >>>implementation, then that too should be part of the public > > >description. > > > >>> > > > >>> Perhaps another aspect concerns the on-the-wire vs. resource > > model > > > >>>of service semantics. In the resource pov, issues of > > implementation > > > >>>(transparent or otherwise) figure prominently. In the > > on-the-wire > > > >>>pov, you only look at the message traffic; and do not > > even consider > > > >>>the implementation. > > > >>> > > > >>> They are related of course: a message is valid if it is well > > formed > > > >>>(in some communication language) and if the implied > predicate is > > > >>>satisfied (there really is money in your bank account). > > > >>> > > > >>> But, a Service Oriented Semantics (SOS) would focus on the > > on-the- > > > >>> wire interpretation and require that the service participants > > > >>>faithfully reflect the messages in their systems. I.e., it is > > similar > > > >>>to the model/proof theory distinction: provided that > the service > > > >>>implementation is a correct Interpretation of the > communication, > > the > > > >>>participants can focus on the Formulae being communicated. > > > >>> > > > >>>That all being said, there are definite limits to descriptions. > > I.e., > > > >>>there will always be unstated (unstateable?) assumptions > > that are > > > >>>required to be shared for successful interactions. > > > >>> > > > >>>Frank > > > >>> > > > >>>On Jul 11, 2005, at 12:49 PM, Ken Laskey wrote: > > > >>> > > > >>>>Frank, > > > >>>> > > > >>>>Opacity/transparency is not a dimension on which to > distinguish > > > >>>>services; it is more of a fallacy that we may need to > > explain our > > > >>>>way around. This ties in very much with what I've > tried to say > > > >>>>about metadata and how metadata characterizing an instance is > > often > > > >>>>the basis upon which the instance is evaluated in the > > context of > > > >>>>assumptions, constraints, and policies (a/c/p) of > providers and > > > >>>>consumers. In some circumstances, the amount of > > information that > > > >>>>needs to be published about an entity may maintain > > little in the > > > >>>>way of its opacity, but that is more likely related to > > a/c/p than > > > >>>>it is to WSDL. > > > >>>> > > > >>>>See more inline. > > > >>>> > > > >>>>At 03:23 PM 7/11/2005, Frank McCabe wrote: > > > >>>> > > > >>>>>I read the revised section on services. And an issue > > that made me > > > >>>>>uneasy before has resurfaced -- about opacity. > > > >>>>> > > > >>>>>I think that the opacity/transparency dimension is not a good > > basis > > > >>>>>for distinguishing services. I am aware of the > intuition: that > > > >>>>>somehow when you use a service you should not have to > > worry about > > >the > > > >>>>>implementation. But what does it mean to say: "the > > implementation > > >is > > > >>>>>hidden from the service consumer"? If the service is > > to add lists > > >of > > > >>>>>numbers then its implementation is hidden provided > numbers are > > >added > > > >>>>>up correctly. (I.e., we should not care about whether > > its in C++ > > or > > > >>>>>C#; multi-threaded or federated). > > > >>>> > > > >>>>So here the service adds numbers and while we can > > imagine what is > > > >>>>happening, we care no more of the specific than we do when we > > punch > > > >>>>numbers into a calculator. > > > >>>> > > > >>>> > > > >>>>>But, some services are explicitly about > implementation issues: > > > >>>>>security services, workload distribution services, > java remote > > > >>>>>execution engine services etc. etc. I.e., it is of > the essence > > that > > > >>>>>to use a Java remote execution service, you have to send it a > > java > > > >>>>>class to execute. In that sense, the implementation is > > critical. > > > >>>> > > > >>>>But you call a java remote execution engine when you have an > > > >>>>appropriate java class to execute. If it is a general service > > that > > > >>>>is implemented as a java remote execution then the WS > interface > > > >>>>should more likely be a collector of information that > > (inside the > > > >>>>service) is rewritten as the necessary java class. You could > > > >>>>require a java class as input but I'm not sure that would be > > > >>>>considered "good style". > > > >>>> > > > >>>> > > > >>>>>A clearer distinction is public/private. A service is > > characterized > > > >>>>>by a public description of its functionality. The public > > >description > > > >>>>>should be sufficient to be able to successfully > > interact with the > > > >>>>>service; and no additional information should be required. > > > >>>> > > > >>>>Not really because what you consider part of the private > > > >>>>information I might consider very pertinent to > deciding whether > > > >>>>your service is suitable for my purposes, i.e. I need > it to be > > > >>>>public. For an extreme example, I used to work for > > your company > > > >>>>and I know one of your developers is clearly > > incompetent and I'd > > > >>>>never use anything that idiot touched. > > > >>>> > > > >>>>The challenge is in defining "should be sufficient to > > be able to > > > >>>>successfully interact with the service". I think we need to > > > >>>>discuss opacity in these terms because it is strongly > connected > > > >>>>with SOA and may be more useful as a vague concept than as an > > > >>>>absolute measure. > > > >>>> > > > >>>> > > > >>>>>Frank > > > >>>> > > > >>>>Ken > > > >>>> > > > >>>> > > > >>>> > > > >>>> > > > >>>> > > > >>>> > > > >>>>-- > > > >>>> > > > > > >>>>---------------------------------------------------------- > > ---------- > > >-- > > > >>>>----------- > > > >>>> / Ken > > > >>>>Laskey > > > >>>>\ > > > >>>> | MITRE Corporation, M/S H305 phone: 703-983-7934 | > > > >>>> | 7515 Colshire Drive fax: > > > >>>>703-983-1379 | > > > >>>> \ McLean VA > > > >>>>22102-7508 / > > > >>>> > > > > > >>>>---------------------------------------------------------- > > ---------- > > >-- > > > >>>>------------ > > > >> > > > >>-- > > > > > >>------------------------------------------------------------ > > ---------- > > >----------- > > > >> / Ken > > > >> Laskey > > >\ > > > >> | MITRE Corporation, M/S H305 phone: 703-983-7934 | > > > >> | 7515 Colshire Drive fax: > > 703-983-1379 > > >| > > > >> \ McLean VA 22102-7508 > > >/ > > > > > >>------------------------------------------------------------ > > ---------- > > >------------ > > > >> > > > >> > > > > > > > > > > > > > >-- > > > > > >------------------------------------------------------------- > > ---------- > > - > > >--------- > > > / Ken > > >Laskey > > \ > > > | MITRE Corporation, M/S H305 phone: 703-983-7934 | > > > | 7515 Colshire Drive fax: > 703-983-1379 > > | > > > \ McLean VA 22102-7508 > > >/ > > > > > >------------------------------------------------------------- > > ---------- > > - > > >---------- > > > > > > >
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