The service that originates a message in this case
is also the entity that processes the response that has exchanged hands until the circle has been
completed. This approach avoids the need for a service controller or proxy by which messages
are coordinated and dispatched by a single entity. Therefore, transaction activities that employ
the circular message delivery approach typically reduce unnecessary message round trips and
reduce network traffic. The circular activity, however, can increase the risk of communication
breakdown between services and consumers, because the passed information must be handled
by several services. In addition, this method must always be a sequential process because each
activity step ought to be completed before the next request is issued.
Exhibit 14.19 depicts a circular activity that accomplishes a page-rendering process, by
which a page is composed from articles and columns provided by the illustrated article and
the column atomic services, respectively. Note that the message originator??”the page renderer
composite service??”is also the receiving end that accepts a compiled page from the page composer
composite service.
Hierarchical Transaction. Recall that hierarchical design compositions depend on the special
parent/child relationships they form. The top-level entity in a hierarchical logical design is the
most general asset. Conversely, lower levels are finer-grained services.
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