- From: Francis McCabe <fgm@fla.fujitsu.com>
- Date: Mon, 17 Feb 2003 14:04:07 -0800
- To: www-ws-arch@w3.org
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 Monday, 17 February 2003 17:05:23 UTC