Thus, each supporting beam can be combined with four logical service design
associations: apparent unidirectional, apparent bidirectional, implied unidirectional, and implied
bidirectional. Exhibit 13.6 illustrates the four possible network beam symbols.
CIRCULAR DESIGN COMPOSITION STYLE. The circular design composition style depicts a sequence
of events, each of which is represented by a single service in a series. Imagine a number
of chained services that are linked by some business or technological association. The message
originator service hands over the first message to the next receiving service. Subsequent delivered
messages always engage the next service in the chain. When this transaction has been completed,
the resulting message arrives back at the starting point.
The circular composition style reduces network traffic by avoiding unnecessary intermediate
message round trips to a centralized service. Instead, messages are handed from one service to
another until the response is delivered to the message originator. In addition, the circular chained
message delivery style involves a number of services that share the transaction processing burden,
rather than applying the strain to a single service.
Strategically, this style addresses the centralization deficiency that is typically introduced
by enabling a single software asset to control message transmission and routing between message
exchange parties.
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