In examining the example, notice that the participating service structures
are associated by their generalization aspect. That is, the root tree??”the investment account
atomic service that is positioned at level 1??”is the top-level service that generalizes the idea
of investment accounts. Right underneath is the fixed-income account composite service and the
annuities service cluster. These are finer-grained offerings that present specific and detailed implementation.
Thus, in descending farther down the hierarchy tree, the service functionality offered
becomes more explicit. Note that this hierarchical structure is supported by hierarchical beams.
This hierarchical arrangement is identified as vertical because of the parent/child affiliation
and their mutual dependencies. Vertical means that messages are being passed between parents
and their offspring, and the business execution is confined to a narrower problem domain. Here,
Service-Oriented Design Composition Styles 265
Investment
Account
Atomic Service
Annuities
Service
Cluster
Level 1
Level 2
Level 3
Fixed Income
Account
Composite
Service
Individual Bonds
Service Cluster
CDs
Composite
Service
EXHIBIT 13.9 HIERARCHICAL DESIGN COMPOSITION STYLE ALONG WITH HIERARCHICAL BEAMS
the revealed business commonality accentuates investment accounts. Thus, this vertical design
composition style would preclude anyone??™s ability to observe a larger scope of the organizational
problem.
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