Week 5 notes

Class Diagrams Overview

• Definition: A UML diagram that outlines objects and their relationships in a system.

• Purpose:

  • Helps in understanding and planning the system.

  • Acts as a technical communication document between teams.

  • Illustrates data models for information systems.

  • Helps coordinate a long-term system vision.

2. Class Diagram Structure

• Basic Elements:

  • Class Name

  • Attributes (characteristics of the class)

  • Methods (Operations) (functions performed by the class)

• Object vs. Class:

  • Class: A logical group of objects with common attributes, relationships, and behaviors.

  • Object: An instance of a class with a defined role, state, behavior, and unique identity.

3. Operations in Class Diagrams

• Definition: Functions or services provided by all instances of a class.

• Types:

  1. Constructor – Creates a new instance of a class.

  2. Query – Accesses an object’s state without modifying it.

  3. Update – Alters an object’s state.

  4. Class-Scope – Applies to a class rather than an individual object.

4. Relationships in Class Diagrams

• Association: A relationship among instances of object classes.

  • Association Role: The name given to the connection between classes.

  • Association Name vs. Association Role:

    • Either can be used, but at least one must be present.

    • Roles appear at both ends of the association.

    • Names go between classes, sometimes with an arrow to indicate direction.

• Multiplicity: Defines how many instances of one class can be associated with another class.

  • Example:

    • "A customer can place multiple orders" → 1:* multiplicity.

• Structural Links:

  • A solid line between two classes represents an association.

5. Encapsulation

• Definition: Hiding the internal implementation of an object from external access.

• Purpose: Protects data and ensures controlled access.

• Example:

  • Private attributes and public methods in a class.