- From: David Orchard <dorchard@bea.com>
- Date: Tue, 18 Feb 2003 12:59:09 -0800
- To: "'Cutler, Roger \(RogerCutler\)'" <RogerCutler@chevrontexaco.com>, <www-ws-arch@w3.org>
- Message-ID: <00e701c2d790$95512220$f10ba8c0@beasys.com>
I agree completely. And the way that I think this should go is as follows: 1. The W3C TAG should darned well write up what a resource is from a web architecture perspective. 2. The WS-Arch group ought to relate a service to a resource *somehow* 3. Both groups get feedback on their definitions. I don't think it makes a great deal of sense for the ws-arch group to worry about defining what a resource is, that ought to be part of the TAG's job. Maybe ws-arch should make a comment on the Web arch document saying "hey, we're trying to figure out how services relate to resources, and you guys need to provide a definition." Cheers, Dave > -----Original Message----- > From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org]On > Behalf Of Cutler, Roger (RogerCutler) > Sent: Tuesday, February 18, 2003 9:52 AM > To: www-ws-arch@w3.org > Subject: RE: Issues, trout ponds and other dangerous regions > > > > I don't entirely understand this discussion, but it sounds to me like > David and Frank have rather different conceptions of what the words > "service" and "resource" mean. If so, it seems to me that it > would be a > good idea to get on the same page somehow. > > -----Original Message----- > From: David Orchard [mailto:dorchard@bea.com] > Sent: Monday, February 17, 2003 6:12 PM > To: www-ws-arch@w3.org > Subject: RE: Issues, trout ponds and other dangerous regions > > > > 0. In general, I'm not really sure what changes you are suggesting to > the text or approach that I took. I get the point #1 about GET/POST, > perhaps there's too much. But on the other ones, it's almost like you > are saying that describing the architectural style of SOA is > a bad thing > to do. I think you are implying that services and resources are > separate things, therefore can't and shouldn't be > compared/constrasted. > Also that the generic vs specific interface is a can 'o worms, so we > shouldn't talk about it. I must admit I'm astounded by our groups > ability to talk about things that we want to talk about. > eek. Now I'm > talking about us talking about us talking about something. I was just > hoping to write up something that could appear in our actual text, > rather than debating whether we should do the text or not. > I'll try to > explain in the rest of this note, my motivations. > > 1. I make the assumption that there is something architecturally to > define about Web services. Given that it is technologically > neutral, it > is probably an architectural style that Web services are. I "bang on > about" POST/GET for illustrative purposes mostly. Indeed, I > specifically chose the nefarious getStockQuote to allow the > description > of the style to "fess up" about it's constraints, and how they are > different and similar to REST. <hint>I think that TAG will give pretty > strong pushback on a ws-arch that doesn't describe it's > architecture in > relation to web architecture. Saying "xml, uris, maybe soap, > maybe wsdl > won't cut it". BTW, I would vote this way on the TAG if > asked - and I'm > SURE somebody will ask the TAG. I just happen to take enough personal > responsibility that I think I should volunteer to help provide such a > description to avoid such pushback. Of course, the ws-arch > could ignore > such TAG feedback. Maybe the Director will even let it pass. But why > cause more trouble for ourselves than we need to</hint> > > 2. I would like to end up with a description of the > architectural style, > and the trade-offs associated with that style. These > trade-offs must be > based upon requirements or properties. Given that the usual criticism > of Web services has been by "REST" folks, I thought that > coming up with > a description and trade-offs in the same vernacular that is > used for the > only real definition of REST would be helpful in getting to > consensus on > similiarities/differences. Hence the choice to use the > properties from > Roy's thesis as the basis for description of properties for SOA, and > hence the choice of trade-offs in the same style that Roy uses in his > sections 4 and 5. Further, I'm lazy. So therefore, I chose to re-use > Roy's properties and architectural style descriptions, rather than > recreate the description of REST in some third party methodology. > > 3. I would like to end up with a harmonized Web architecture and Web > Services architecture, from glossary terms to styles discussions to > properties. I really do believe that this is possible. BTW, > when I say > "harmonized", I specifically mean that there are references from web > services arch to web arch, and it includes > changes/extensions/refinements to web arch "things". I HIGHLY doubt > that the TAG is going to choose a vendor-specific architecture > methodology. So we need to find some way of getting to a common > methodology. Again, I simply don't have the time or energy to come up > with yet another darned methodology. > > 4. I think that the definition of "Resource" as an entity that has > actual presence is not a widely accepted definition. I find > it somewhat > interesting that the URI spec does not define what Resources are, and > leaves it to something like RDF, which says > > "Resources All things being described by RDF expressions are called > resources. A resource may be an entire Web page; such as the HTML > document "http://www.w3.org/Overview.html" for example. A resource may > be a part of a Web page; e.g. a specific HTML or XML element > within the > document source. A resource may also be a whole collection of pages; > e.g. an entire Web site. A resource may also be an object that is not > directly accessible via the Web; e.g. a printed book. Resources are > always named by URIs plus optional anchor ids (see [URI]). > Anything can > have a URI; the extensibility of URIs allows the introduction of > identifiers for any entity imaginable. " > > So there doesn't appear to be anything that's not a resource. It's > anything imaginable. It's fairly easy for me to see that a > Web service > is ALWAYS a resource. It's a particular type of a resource, > as noted in > our definition which says that a Web service is identified by > a URI - a > Web service is identified by a URI, URIs are for Resources, > therefore a > Web services is a resource. > > 5. Are you saying that a Service MUST have a description, > otherwise it's > not a service? Do you mean a WSDL realization of that > description? And > how is that *REALLY* different than the web? Each web page > that I look > describes to me how to use it - otherwise I wouldn't know > which links to > select! :-) I have been trying to avoid the requirement that a service > has a formal description. And saying a web service is describable in > WSDL is I think terrible as well - as WSDL can describe anything that > the group chooses to describe! > > 6. I don't get the distinction between service provider and resource > provider. See my item #4 on the relationship between resources and > services. > > 7. As for generic vs specific, I don't think it's a can of worms to > describe it, or the benefits. Where I expect, and have > already gotten, > the pushback is when some of the benefits acrue. As in, > "some kinds of > applications are better styled in a SOA" manner, with the pushback of > "oh yeah, I've never seen one". BTW, I'm hoping that the > comparison of > a few different use cases of app development will flesh out the point > that you are making, that is the the objects and verbs must both be > understood. This shows up in the visibility property elaboration. > Course, while I spend time justifying what I'm doing, I can't actually > be doing the doing of the scenarios, SOA references etc. > > Cheers, > Dave > > > -----Original Message----- > > From: www-ws-arch-request@w3.org > [mailto:www-ws-arch-request@w3.org]On > > Behalf Of Francis McCabe > > Sent: Monday, February 17, 2003 2:04 PM > > To: www-ws-arch@w3.org > > Subject: Issues, trout ponds and other dangerous regions > > > > > > > > David gives an eloquent defense of REST in > > [http://www.w3.org/2002/02/mid/ > > 007d01c2d325$5c30fc00$c10ba8c0@beasys.com;list=www-ws-arch]; > > however it > > appears that he re-opens issues that need resolving. > > > > In the current WSA document, in several places, it is > stated that Web > > services are NOT tied to specific technologies and protocols > > (such as > > HTTP, SOAP, WSDL etc.) In fact, currently, the ONLY hard nailed-down > > technology choices are URIs and XML. > > > > If the WSA is to be technology neutral, then it is not > appropriate to > > `bang on about' POST vs GET in the document; although > > constraints such > > as idempotency are definitely `in scope'. On the other hand, > > if the WSA > > is to be technology centered, then we need to make that choice > > explicit, and soon. > > > > The second nettle is more conceptual: the distinction between > > resources and services. There is a relationship, but > perhaps not one > > that is immediately obvious. In my opinion these concepts are at > > different levels of abstraction: a resource is an entity > that has an > > actual presence and a service is a means of achieving tasks. > > Services require > > realizations, and such realizations are resources; but > > resources can be > > `of' anything and are not tied to services. On the other > > hand, services > > have descriptions which are not of the service itself but of how to > > interact with them. > > > > This distinction is important because, if the focus is on > services as > > opposed to resources, then a large number of concepts need to > > be `put > > into place' that have no relevance to the strict resource > > view. A good > > example is the service provider. It is an important concept for a > > service oriented architecture; but has no special equivalent for > > resource. (Owner, however, is a concept that applies to both.) > > > > Finally, there is the hoary old one concerning generic > interfaces vs. > > specific interfaces. Again, so far, we have been pretty > > muddled about > > this. [Personal opinion: it is not possible to completely > > capture the > > semantics of a message without grasping both the verb and the > > object of > > the message. Definitely there are different styles of architecture, > > where there is a rich though generic set of verbs that everyone is > > expected to agree on, and where there is an essentially > > infinite set of > > verbs and everyone is expected to come up with their own > > definitions. I > > am somewhat persuaded of the merits of the generic case; but > > its a can > > o'worms defining the spanning set.] > > > > > > > >
Received on Tuesday, 18 February 2003 16:01:47 UTC