Page 103 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Unit 8: Advanced Interaction Modelling

unit, we will discuss use case relationships, procedural sequence model, and special constructs Notes
for activity models.

8.1 Use Case Relationships

Use cases share different kinds of relationships. A relationship between two use cases is basically
a dependency between the two use cases. Defining the relationship between two use cases is the
decision of the modeler of the use case diagram.

Did u know? The use of an existing use case using different types of relationships reduces
the overall effort required in defining use cases in a system.
Use case relationships can be one of the following:

8.1.1 Communicates

The participation of an actor in a use case is shown by connecting the actor symbol to use case
symbol by a solid path. The actor is said to ‘communicate’ with the use case. This is only relation
between an actor and use cases. See figure 8.1.

Figure 8.1: Communicates Relationship

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

8.1.2 Extends

An ‘extends’ shows the relationships between use cases. Relationship between use case A and
use case B indicates that an instance of use case B may include (subject to specified in the extension)
the behavior specified by A. An ‘extends’ relationship between use cases is depicted with a
directed arrow having a dotted shaft. The tip of arrowhead points to the parent use case and the
child use case is connected at the base of the arrow. The stereotype “<extends>” identifies as an
extend relationship.
For example, validating the user for a system. An invalid password is extension of validating
password use case as shown in figure 8.2.

Figure 8.2: An Example of an Extend Relationship

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

8.1.3 Include or Uses

When a use case is depicted as using functionality of another functionality of another use case,
this relationship between the use cases is named as an include or uses relationship. A uses

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