O

Farmer

Get Weather Data

Figure 5-5. Example of a bidirectional use case.

additional reviewers in the case that the document deals with issues that none of the reviewers is a specialist in the field. Figure 5-6 shows the use case model for the department chair approval process.

In this figure, the use case Add Reviewer extends the base use case Approve Document. According to the problem description, the department chair can add an additional reviewer to a document when he judges that a more specialized reviewer should review the document. This means that normally, the department chair considers that reviewers assigned to the document are sufficient. Thus, the description of the base use case Approve Document is independent of the use case Add Reviewer. The base use case can be executed without involving the extend use case. The functionality provided by the extend use case Add Reviewer is needed only under certain conditions, when the department chair finds it necessary.

Department Chair

Approve Document

Figure 5-6. Use case Add Reviewer extends base use case Approve Document.

Department Chair

Approve Document

Figure 5-6. Use case Add Reviewer extends base use case Approve Document.

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