Page 87 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Unit 7: Interaction Modelling

It is convenient to consider the graphical component of a use case as a kind of table of contents Notes
that directs the reader to the accompanying text.

Example: In Figure 7.1, the most basic form of a use case is represented graphically by a
named task oval that represents a user goal. This diagram illustrates a customer’s ability to
Login and to make booking. As more detail becomes available, it is added to the use case.
Figure 7.1: A Simple use Case Model, Featuring an Actor,
Two Task Ovals, with Associations

!
Caution Over time, the use case becomes primarily a textural construct that describes the
system behaviour in semi-formalised natural language.

7.1.1 Use Case Concept

A use case diagram is used to graphically depict a subset of the model to simplify communications.
There will typically be several use case diagrams associated with a given model, each showing
a subset of the model elements relevant for a particular purpose. The same model element may
be shown on several use case diagrams, but each instance must be consistent. If tools are used to
maintain the use case model, this consistency constraint is automated so that any changes to the
model element will be automatically reflected on every use case diagram that shows that element.
The use case model may contain packages that are used to structure the model to simplify
analysis, communications, navigation, development, maintenance and planning.

Much of the use case model is in fact textual, with the text captured in the use case specifications
that are associated with each use case model element. These specifications describe the flow of
events of the use case.
The use case model serves as a unifying thread throughout system development. It is used as the
primary specification of the functional requirements for the system, as the basis for analysis and
design, as an input to iteration planning, as the basis of defining test cases and as the basis for
user documentation.

7.1.2 Basic Model Elements

The use case model contains, as a minimum, the following basic model elements:
Actor: A model element representing each actor. Properties include the actors name and
brief description.

LOVELY PROFESSIONAL UNIVERSITY 81