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Organizing principles for services

One of the questions that comes up from time to time is how to define your services. This has come up for me in two independent fora: within the OASIS Service Oriented Architecture work and in the context of human provided services, for example at Genietown.

In the work on the SOA Reference Model we decided that "services are the mechanism by which needs and capabilities are brought together"; i.e., its about needs and capabilities to satisfy those needs, and the access mechanism.

However, this still begs the question somewhat. In the domain of human services, where the services are things like "building a home", "walking the dog", "taking care of my elderly parents"; it gets even fuzzier. Sometimes a service seems to organized around the person offering the service, for example, an architect, or a doctor. Sometimes the service is organized around a particular kind of product, such as doors or skylights. At other times, the service is organized around a material, such as glazing and paint services. Another kind of organizing principle is location; for example, landscape services involve a whole range of things in the garden.

While it is clear that a service is typically organized around a set of actions, and one or more resources; I do not believe that there is a single 'syntactic' condition that can be applied to define a service.

Currently, we do not have a good higher-level handle on how to organize a large suite of resources and actions into well differentiated services. The standard technologist's answer to all this is to throw the problem 'upstairs' and appeal to business function (e.g., accounts, sales, library book management etc.). What that amounts to is asking someone else to come up with the organizing principles for defining a service. It may just be that the business level is the right level to ask these questions.

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