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Subject: The Service Interface
Folks, I'm in the process of crafting a UML component diagram for the Service Description artifact, but we need to nail down the notion of Service Interface before I proceed. I don't want to indulge into endless debate here, I just want to know what is the minimum set of service implementation-independent things needed in order for a consumer agent to communicate with a provider agent (i.e., service). I happen to like Wikipedia's general definition of interface which states that "An interface defines the communication boundary between two entities, such as a piece of software, a hardware device, or a user." Of course for the RA, we're talking about software interfaces that exist between separate software components that provide a mechanism by which the components communicate (consumer agents and provider agents/services) and not user interfaces per se. We should perhaps extend that notion to physical interfaces as well, i.e., interfaces between hardware components because there is an evolving world of things like XML gateways out there. The WSA defines a service interface as follows: "A service interface is the abstract boundary that a service exposes. It defines the types of messages and the message exchange patterns that are involved in interacting with the service, together with any conditions implied by those messages." In terms of relationships to other elements, it goes on to say a service interface defines "the messages relevant to the service." The explanation states "A service interface defines the different types of messages that a service sends and receives, along with the message exchange patterns that may be used." So is only a subset of the Information Model and Behavior Model enough, i.e., messages and MEPs? What about service bindings (), endpoints, operations, faults, etc. Do they have a role in the service interface. In other words, are these examples of service implementation-independent things that are necessary the consumer agent to communicate with the provider agent/service? In terms of the RM and RA, are there elements of Service Reachability at play? Whatever we agree on, we should be able to map to concrete examples (just to check our own sanity of course and not to include in the actual RA spec.) say one from the Web services world using WSDL 1.x and 2.0, and perhaps one from the CORBA IDL world. Note that in the WSDL 2.0 world, the service interface defines what abstract "functionality" a Web service provides and the binding describes how to access the service. In the RM and RA, we currently model Service Functionality separate from Service Interface. Interested in your thoughts. Pragmatic ones, please! Cheers... - Jeff E., JPL
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