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Chapter 5. Understanding distribution of responsibility 91
The insights gained by modeling the various elements (for example, analysis
subsystems, localities) can lead to their refactoring and refinement until the
needed set of interactions are identified and assigned to them. The candidate
operations can also be refactored and refined as a result of the insights gained
from the model.
Next, we must link the information in the JRT to a model of the system. To do so,
it is necessary to identify the subsets of operations that are performed by a
particular locality. Examples from the JRT are the Receive Data Block
operations, which are performed by both the I/O Services subsystem and the
Printer Control Unit locality. An initial set of interfaces can be derived by
considering the mapping of operations to localities. In addition, cohesion
principles should be applied to specify interfaces and then the mapping of
operations to localities should be used as a check to ensure that the minimum
requirement (the
split of operations across localities for a given analysis
subsystem) is satisfied. The resulting analysis-level logical and distribution views
are shown in Figure 5-6.
Figure 5-6 Association of logical entities, localities, and interfaces