Class Diagrams: Identifying and Representing Classes, Slides of Object Oriented Analysis and Design

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Class Diagrams

Identifying and representing Classes

How many classes

Many Classes

Classes have simple behavior Less encapsulation More reusable Easier to Implement

Few Complex Classes

More encapsulation, more private behavior. Less reusable Takes more time to implement More complex to implement

Class Design Step

Define

Class Operations Methods States Attributes Dependencies Associations Generalizations

Simple steps in finding a class

Read and understand the specification.

Extract noun phrases from the specification

and build a list.

Look for nouns that may be hidden (for

example, by the use of the passive voice), and

add them to the list.

Applying the following guidelines:

Model Physical Objects. Model Conceptual Entities. Use a Single term for each concept. Be wary of the use of adjectives.

Attributes & Operations

Find responsibilities using the following

guidelines:

Recall the purpose of each class, as implied by its name and specified in the statement of purpose. Extract responsibilities from the specification by looking for actions and information. Identify responsibilities implied by the relationships between classes.

… Attributes & Operations

Assign responsibilities to classes using the

following guidelines:

Evenly distributed system intelligence. State responsibility as generally as possible. Keep behavior with related information. Keep information about one thing in one place. Share responsibilities among related classes.