Page 92 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Object Oriented Analysis and Design

Notes They focus on message sequences, that is, how messages are sent and received among
number of objects.

Sequence diagrams have two axes: the vertical axis shows time and the horizontal axis
shows a set of objects.
The instance form describes a specific scenario in detail.

The Generic form describes all possible alternatives in a scenario, therefore branches,
conditions, and loops may be included.
Sequence diagrams describe interactions among classes in terms of an exchange of messages
over time.

Notes Historically, Charles Babbage was the first person to draw a diagram where each
part of a machine was shown as a vertical line, time flows down the page, and connections
between the parts flow across the page. This idea has been reinvented several times in the
last 10 years.

7.2.1 Basic Sequence Diagram Symbols and Notations

Class roles: Class roles describe the way an object will behave in context. Use the UML object
symbol to illustrate class roles, but don’t list object attributes.
Figure 7.6: Class Roles

Activation: Activation boxes represent the time an object needs to complete a task.

Figure 7.7: Activations

Messages: Messages are arrows that represent communication between objects. Use half-arrowed
lines to represent asynchronous messages.

!
Caution Asynchronous messages are sent from an object that will not wait for a response
from the receiver before continuing its tasks.

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