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Subject: RE: [soa-rm] Opacity calumny
> It may act in both the client and the server capacities but > it doesn't have to. Agree. It's all up to requirements. Joe Joseph Chiusano Booz Allen Hamilton O: 703-902-6923 C: 202-251-0731 Visit us online@ http://www.boozallen.com > -----Original Message----- > From: Ken Laskey [mailto:klaskey@mitre.org] > Sent: Wednesday, July 13, 2005 10:11 AM > To: Chiusano Joseph; soa-rm@lists.oasis-open.org > Subject: RE: [soa-rm] Opacity calumny > > It may act in both the client and the server capacities but > it doesn't have to. I know of an example where a DoD system > had a huge number of APIs (I seem to remember 1200) and they > had a utility that generated WSDLs for each one and said > they've complied with making things visible and accessible > because here were your Web services. > > Somehow that seems like complying with the letter of the law > without serving the spirit or furthering the intent. > > Ken > > At 09:49 AM 7/13/2005, Chiusano Joseph wrote: > > > 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 > > > > >/ > > > > > > > > > >------------------------------------------------------------- > > > > ---------- > > > > - > > > > >---------- > > > > > > > > > > > > > > > > > -- > > -------------------------------------------------------------- > ------------------- > / 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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