Analysis Patterns by Martin Fowler

Author:Martin Fowler
Language: eng
Format: epub, pdf
Publisher: Pearson Education Limited (US titles)
Published: 1997-03-11T16:00:00+00:00

8.5.1 Plans and Protocols as Graphs

We can also represent a plan as a directed acyclic graph (DAG) of proposed actions. The arcs on the graph correspond to the dependency relationships on the action references. Each plan has its own separate graph structure. We can represent this compactly as shown in Figure 8.11. This is, in essence, another association pattern in the style described in Chapter 15.

Figure 8.11 Plan as a directed acyclic graph of proposed actions.

To apply this notion to a protocol, however, we do not form a DAG of the subsidiary protocols. Instead we form a DAG of the protocol references, as shown in Figure 8.12, because one protocol can appear as more than one step in another parent protocol. This is specifically not the case for a plan due to the uniqueness constraint shown in Figure 8.6. The base form for a DAG association pattern thus includes the dependency types (with the constraint) together with the fact that the element in the DAG can only appear as one node in a DAG.

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