Page 105 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Unit 8: Advanced Interaction Modelling

Notes
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Caution The parent use case in an extend relationship can’t be replaced by the child use
case.

Figure 8.4: An example of Generalization Relationship

Source: http://gyan.frcrce.ac.in/~surve/OOAD/UCD/UCD_Relationships.html

From the diagram of a generalization relationship (Figure 8.4), you can that
“Store_patient_records (paper file)” (parent) use case is depicted as a generalized version of the
“Store_patient_records (computerized file)” (child) use case. Defining a generalization
relationship between two implies that any occurrence of “Store_patient_records (paper file)”
use case in the business flow of the system can be replaced with the “Store_patient_records
(computerized file)” use case without impacting any business flow. This means that in future
you might choose to store patient records in a computerized file instead of as paper documents
without impacting other business actions.

Example: Consider example of Invalid Password use case which is extension of Login
use case. The Login use case can’t be replaced by Invalid Password use case. If you try to do this,
you would not be able to seamlessly replace the occurrence of the “Login” use case with “Invalid
Password” use case.

Task Make distinction between ‘communicates’ and ‘generalization’ relationship.

Notes In general, a child revises behavior subsequences at several different points of the
parent sequence.

Self Assessment

Fill in the blanks:

1. Defining the relationship between two use cases is the decision of the ................... of the use
case diagram.
2. A ................... between two use cases is basically a dependency between the two use cases.

3. ................... is only relation between an actor and use cases.
4. A ‘...................’ relationship between use cases is depicted with a directed arrow having a
dotted shaft.

5. In an ................... relationship, a use case includes the functionality described in another
use case as a part of its business process flow.

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