Class Models

Class Models
for Engineering Design

Computer Science Department

bernstdh@jmu.edu

Overview

Class Models for Engineering Design

Purpose:
- Illustrate the specifications for the static structure of classes and interfaces
Enhineering Models vs. Conceptual Models:
- A conceptual model represent real-world concepts
- An engineering design model represent software components

Contents of Class Models for Engineering Design

The Process

Classes in UML

The Basics

Classes in UML (cont.)

Visibility

Relationships: Association

Definition:
- Class A is said to be associated with class B if an object in class A can send a message to an object of class B or if an object in class A can create, receive or return objects of class B.
Set Theoretic Concepts:
- ?

Relationships: Dependency

Definition:
- Class A is said to depend on class B if method in an object of class A is passed an object of class B.
Dependency or Association?
- A dependency is a special types of association

Relationships: Specialization

Definition:
- An object of class A "is-an" object of class B if A is/does everything that B is/does and more.
Set Theoretic Concepts:
- Subset and superset

Relationships: Aggregation

Definition:
- An object of class A "has-an" object of class B if B is a part of A.
Set Theoretic Concepts:
- Union?

Relationships: Composition

Definition:
- An object of class A is composed of an object of class B if B is a part of A and A controls the life of B (e.g., if A is destroyed then B will be destroyed). Thus a component can be associated with exactly one composite (making the multiplicity implictly 1).
Set Theoretic Concepts:
- Union plus?

Interfaces in UML

Defined:
- A set of operations/services
Implications:
- A class that implements/realizes an interface promises that it will implement all of the methods in the interface
- A class that implements/realizes an interface has an "is a" relationship with that interface

Interfaces in UML (cont.)

An Example

There's Always More to Learn