Page 91 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Unit 7: Interaction Modelling

Notes
Example: An order must always have a customer number.
Scenarios: Formal, sequential descriptions of the steps taken to carry out the use case, or
the flow of events that occur during a Use Case instance. These can include multiple
scenarios, to cater for exceptional circumstances and alternative processing paths. These
are usually created in text and correspond to a textual representation of the Sequence
Diagram.
Scenario diagrams: Sequence diagrams to depict the workflow; similar to Scenarios but
graphically portrayed.

Additional attributes, such as implementation phase, version number, complexity rating,
stereotype and status.

Actors

Use Cases are typically related to ‘actors’, which are human or machine entities that use or
interact with the system to perform a piece of meaningful work that helps them to achieve a
goal. The set of Use Cases an actor has access to define their overall role in the system and the
scope of their action.
Figure 7.5: Actor

Self Assessment

Fill in the blanks:
1. A ................... model is a model of how different types of users interact with the system to
solve a problem.
2. A ................... is an instance of a use case, and represents a single path through the use case.
3. ................... are used to describe the relationships between actors and the use cases they
participate in.
4. ................... are typically related to ‘actors’, which are human or machine entities that use
or interact with the system.

5. ................... is used to include optional behavior from an extending use case in an extended
use case.

7.2 Sequence Models

Sequence diagram is the way to explain the behaviour of a system with a view to make interaction
between the system and its surrounded environment. This interaction is arranged in a proper
time sequence.

Sequence diagrams illustrate how objects interact with each other.

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