The Use Case Diagram

The set of all use cases in a problem domain is referred to as the use case model and the diagram representing it is referred to as the use case diagram. A use case model shows the set of functionalities a system should provide. By examining a use case model, we can say whether all the user requirements are satisfied or not. A use case model is important, as it presents a general view of the system without being overwhelmed by implementation details.

Let us consider IFAS's extension document approval system and build the use case model. The following is a brief description of the functionalities the system should provide.

The system should allow users (authors, editors, reviewers, department chairs, and program leaders) to submit, edit, review, approve, and check the status of a document any time. First, the authors should submit the document and then the editor edits it. At the least, two reviewers, assigned to the document, will be notified for reviewing the document. After the reviewer's approval, the department chair is notified to approve the document. If the department chair judges that another and more specialized reviewer should review the document, then a new reviewer can be added. The newly added reviewer will be notified by mail that a document is waiting for approval.

After the additional reviewer approves the document, the department chair is notified by mail that the document is waiting for departmental approval. When the department chair approves the document, the program leader is notified by mail. When the program leader approves the document, then the document is saved in the database and indexed. It becomes public and available for search purposes. The use of the system should be password protected.

The use case model should express all the functionalities required by the system. By examining the use case model one should be able to judge whether all users requirements are correctly captured and whether all user's roles are included in the system. Figure 6-1 shows a simplified use case model for a tracking system for extension documents (http://ers.

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