Thus, the design chosen
should accommodate this hierarchical need to pass messages from parent to child and vice versa.
Another message delivery approach is possible: It may be that the service may need to participate
in transactions that are executed across tree levels. For example, in Exhibit 13.9, the fixed-income
composite service may converse with the annuities service cluster, both located on level 2.
Employ the hierarchical design composition style to leverage the following two major
benefits: (1) Propagation of messages over short distances between family members increases
266 Ch. 13 Service-Oriented Logical Design Composition
message delivery efficiency and improves service performance. (2) The clear division of responsibilities
and roles between higher and lower family tree authorities eases design and architectural
activities. An offspring service is typically responsible for detailed and tactical implementations,
and a parent service is positioned to tackle strategic tasks.
Levels of Execution and Granularity Considerations. Again, the various tree levels are populated
with services on different granularity scales. The higher levels??”meaning the parents??”are
typically coarse-grained entities that characteristically offer more processes and more functionality.
Conversely, the lower levels are occupied by fine-grained assets requiring fewer resources
because of their narrower execution scope.
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