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Jim Waldo on Distributed Computing
A Conversation with Jini's Chief Architect, Jim Waldo
by Frank Sommers with Bill Venners
First Published in JavaWorld, November 2001

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Richer Semantics for Service Discovery

Frank Sommers: Many people working with Jini quickly discover that an object -- a Jini proxy, for instance -- contains data as well as method calls. Currently, Jini provides a fairly limited way to use that data in service discovery. Jini service discovery is based primarily only on Java language type, simple matching of entry attributes associated with a service, and a unique service ID. Do you envision richer semantics for Jini service discovery?

Jim Waldo: I wouldn't say those three are the only means of service discovery. Those are the only ways we guarantee will always exist, but Jini's whole architecture is based on the notion that the infrastructure should be simple, and that the ability to provide value-added services should be easy to do. So, when people say they want much more complicated ways of finding their services, I tell them to write services that offer those complicated ways. You could have another service beyond the Jini lookup service that registers itself in the Jini lookup service, but also takes the contents of that lookup service and organizes it in completely different ways.

Frank Sommers: A data access layer?

Jim Waldo: It could be an access layer, it could be a SQL database on the attributes of the entities in the Jini lookup service. It could be a specialized filter that watches things coming in and informs you of things in which it thinks you might be interested. All those things are possible services. They are not part of the Jini infrastructure because that infrastructure is an attempt to keep things as small and simple as possible, but the Jini infrastructure does enable those services because the information is there and it can find and use them.

Those sorts of services could provide others ways of accessing and massaging that information in a way you find most easily digestible. What you find most easily digestible may not be the same as what other people find most easily digestible, which is another reason we don't provide these kinds of services in Jini, because Jini is trying to be the layer everybody requires. You may have a service that organizes the information in a way you find best. I may have a service that organizes the information in a very different way, which I find best. I shouldn't foist my service off on you, nor should you foist yours on me. That would be incompatible with the Jini philosophy.

By having these things as services, I can, by the way, find your service and see how you view the data in case that might be useful for me, assuming you will allow me to do that.

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