Page 88 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Object Oriented Analysis and Design

Notes Use Case: A model element representing each use case. Properties include the use case
name and use case specification.

Associations: Associations are used to describe the relationships between actors and the
use cases they participate in. This relationship is commonly known as a “communicates-
association”.

Advanced model elements: The use-case model may also contain the following advanced
model elements.

Subject: A model element that represents the boundary of the system of interest.
Use Case Package: A model element used to structure the use case model to simplify
analysis, communications, navigation, and planning. If there are many use cases or actors,
you can use use case packages to further structure the use case model in much the same
manner you use folders or directories to structure the information on your hard-disk.
You can partition a use case model into use case packages for several reasons, including:

To reflect the order, configuration, or delivery units in the finished system thus
supporting iteration planning.

To support parallel development by dividing the problem into bite-sized pieces.
To simplify communication with different stakeholders by creating packages for
containing use cases and actors relevant to a particular stakeholder.

Generalisations: A relationship between actors to support reuse of common properties.
Dependencies: A number of dependency types between use cases are defined in UML. In
particular, <<extend>> and <<include>>.

<<extend>> is used to include optional behavior from an extending use case in an
extended use case.
<<include>> is used to include common behavior from an included use case into a
base use case in order to support reuse of common behavior.
The latter is the most widely used dependency and is useful for:
Factoring out behavior from the base use case that is not necessary for the
understanding of the primary purpose of the use case to simplify communications.
Factoring out behavior that is in common for two or more use cases to maximise
reuse, simplify maintenance and ensure consistency.

Task Make distinction between <<extend>> and <<include>>.

7.1.3 Use Case Diagrams

A use case is a set of scenarios that describing an interaction between a user and a system. A use
case diagram displays the relationship among actors and use cases. The two main components of
a use case diagram are use cases and actors.

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