Jim and Savas on services and resources

Jim writes, regarding a diagram by Savas;

It shows that managing virtualised resources across organisations isn’t scalable, whereas composition of services is. Why the difference in terms of scalability? In the service-oriented view, services can manage whatever backend resources they have for themselves, therefore the complexity of the application driving the services increases linearly with the number of services. In the resource-oriented view, the consuming application must deal with each resource directly and so complexity increases as the sum of a multiple (the number of resources) of each service.

Aside; I think Jim’s using the WS-RF notion of “resource”, which is cool, since it jives so closely with the Web’s notion of one (stateful resource, stateless interaction).

I think the scalability claim above is only correct if you ignore a whole class of useful resources; containers which contain other resources. So I could layout a resource centric view of the network in that diagram to look exactly like the service centric view Savas draws. For example, I might define a container called “the aggregate log ‘file’ of all devices in this building”, and this might be dynamically constructed in basically the same way that aggregate RSS feeds are constructed. And, of course, it would be given a http URI so that I could snarf data from it. Each log entry could also provide the URI of the more granular “device” that it came from so that I, or an automata, could visit there to find its current status.

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