Object Oriented Modeling - Graphic Editor

Step-wise procedure to translate a problem statement into class diagram

Problem Statement

"Develop a graphic editor that can draw different geometric shapes such as line, circle and triangle. User can select, move or rotate a shape. To do so, editor provides user with a menu listing different commands. Individual shapes can be grouped together and can behave as a single shape."

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Step 1). Identify Classes

Extract nouns in the problem statement.

Develop a graphic editor that can draw different geometric shapes such as line, circle and triangle. User can select, move or rotate a shape. To do so, editor provides user with a menu listing different commands. Individual shapes can be grouped together and can behave as a single shape.

Eliminate irrelevant classes.

• Editor - Very broad scope
• User – Out of system boundary
• commands – Broad scope

Add more classes by analyzing requirements

• Group - required to behave as a shape
  • Individual shapes can be grouped together and can behave as a single shape
• View – editor must have a display area

Following classes have been identified:

• Shape
• Line
• Circle
• Triangle
• Menu
• Group
• View

Basic Object Model - Graphic Editor

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Step 2). Identify Associations

Extract verbs connecting objects.

"Individual shapes can be grouped together"

• Group consists of lines, circles, triangles
• Group can also consists of other groups

(Composition)

Verify access paths.

View contains shapes

• View contains lines
• View contains circles
• View contains triangles
• View contains groups

(Aggregation)

Menu sends message to View

(Simple One-Way Association)

Basic Object Model - Graphic Editor

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Step 3). Identify Attributes

Extract properties of the object from the domain knowledge.

• Shape
  • Color
  • Vertices
• Line
  • Color
  • Vertices
  • Length
• Circle
  • Color
  • Vertices
  • Radius
• Triangle
  • Color
  • Vertices
  • Angle
• Menu
  • Name
  • isOpen
• Group
  • noOfObjects
• View
  • noOfObjects
  • selected

Basic Object Model - Graphic Editor

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Step 4). Identify Operations

Extract verbs connected with an object.

Develop a graphic editor that can draw different geometric shapes such as line, circle and triangle. User can select, move or rotate a shape. To do so, editor provides user with a menu listing different commands. Individual shapes can be grouped together and can behave as a single shape.

Eliminate irrelevant operations.

• Develop - out of system boundary
• Provides - have broad semantics
• Behave – broad semantics

Following are selected operations:

• Shape
  • Draw
  • Select
  • Move
  • Rotate
• Line
  • Draw
  • Select
  • Move
  • Rotate
• Circle
  • Draw
  • Select
  • Move
  • Rotate
• Triangle
  • Draw
  • Select
  • Move
  • Rotate
• Menu
  • Open
  • Select
  • Move
  • Rotate
• Group
  • Draw
  • Select
  • Move
  • Rotate

Extract operations using domain knowledge

• View
  • Add
  • Remove
  • Group
  • Show

Basic Object Model - Graphic Editor

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Step 5). Identify Inheritance

Search “is a kind of” by looking at keywords like “such as”, “for example”, etc

"…shapes such as line, circle and triangle…"

• Line, Circle and Triangle inherits from Shape

By analyzing requiremens

"Individual shapes can be grouped together and can behave as a single shape"

• Group inherits from Shape

Refined Object Model - Graphic Editor