It is to facilitate an arbitrary
composition of these services in a declarative fashion, so as to define and publish
more and more composite services. Business Process Management (BPM) tools can
be integrated over ESB to leverage service aggregation and service collaboration.
This facilitate reuse of basic or core (or fine grained) services at the business
process-level. So, granularity of services is important which will also decide the
level of reusability.
Coarse Grained or Composite Services consume Fine Grained Services. Applications
which consume Coarse Grained Services are not exposed to the Fine Grained
Services that they use. Composite Services can be assembled from Coarse Grained as
well as Fine Grained Services.
To make the concept clear, let us take the example of provisioning a new VOIP
Service for a new customer. This is a Composite Service which in turn calls
multiple Coarse Grained Services such as validateOrder, createOrVerifyCustomer, and
checkProductAvailability. Now, createOrVerifyCustomer, the Coarse Grained Service
in turn call multiple Fine Grained Services like validateCustomer, createCustomer,
createBillingAddress, and createMailingAddress.
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