But this may not be a bad thing. In fact, most design implementations should focus on
solutions rather than solving larger issues. Therefore, employ the hierarchical design composition
style to tackle a narrower problem scope by delivering concise and practical solutions.
Service Family Approach to Logical Design. The common approach to associating organizational
service-oriented software assets is to arrange them in hierarchical formations. This
encourages positioning a service based on its family relationship and its dominance in the family
tree. The service family approach not only enables a coherent design strategy, it simplifies the
affiliations between services, and enhances the generalization capability of the involved practitioners
in the design process. Higher levels in hierarchical formation are typically allocated for
more generalized and coarse-grained services. Lower levels are dedicated to finer-grained siblings.
For example, in Exhibit 13.9, the fixed-income account composite service is positioned under its
parent (on level 2), the investment account atomic service (level 1). But at the same time, it is
located one level above its offspring, the individual bonds service cluster (seen on level 3).
The hierarchical design composition style also dictates the method by which services
exchange messages and influences their routing paths. It is conceivable that a service family
member would be likely to communicate with its parents or offspring.
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