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SOA in Practice by Nicolai M. Josuttis

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Composed Services

The second stage of expansion adds composed services. These represent the first category of services that are composed of other services (basic and/or other composed services).

In SOA terminology, composing new services out of existing services is called orchestration. Like in an orchestra, you combine different "instruments" to perform tasks that are more complex than those possible with a single instrument. These services might therefore also be called orchestrated services.

These services operate at a higher level than basic services, but they are still short-term running and conceptually stateless. To use a workflow term, a composed service represents a micro flow, which is a short-running flow of activities (services, in this case) inside one business process.

Note

In [KrafzigBankeSlama04] these kinds of services are called "intermediate services," which is not such a good term because it is not self-explanatory. You have to know what the other categories are to understand what is meant by "intermediate."

Composed Services for Multiple Backends

Composed services are typically services that access multiple backends and therefore are composed of multiple basic services. A typical example is a service that updates redundant data on multiple backends. For example, large systems may contain the same customer data in different backends (in a system local to one company redundant customer data might be found in the CRM and billing systems, while in a system spanning ...

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