Class diagram design

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Lab Manual

CPCS 457

Software engineering theory

1433/1434H

Lab – 6

Design Class diagram

Names I.D.

1. .………..………. ………

2. ………. ………

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LAB objective:

 Overview

 Introduction to class diagram

 Design class diagrams

 How to design a class diagram

 Representing Relationships

 Class diagram example

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Overview

The class diagram is the main building block of object oriented modeling. It is used both for general conceptual modeling of the systematic of the application, and for detailed modeling translating the models into programming code. Class diagrams can also be used for data modeling. The classes in a class diagram represent both the main objects, interactions in the

application and the classes to be programmed.

introduction to class diagram:

class diagram is a type of static structure diagram that describes the structure of a system by showing the system's classes, their

attributes, operations (or methods), and the relationships among the classes.

Class diagram design:

In the diagram, classes are represented with boxes which contain three parts:

 The upper part holds the name of the class

 The middle part contains the attributes of the class

 The bottom part gives the methods or operations the class can take or undertake

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How to design a class diagram:

1- Determine which classes require persistent storage

2- Define persistent classes

3- Represent relationships among persistent classes

4- Choose appropriate data types and value restrictions (if necessary) for each field

Representing Relationships Type of relationships

- 1:1, 1:M, M:M (one-to-one, one-to-many, many-to- many)

- Association class used with M:M

One-to-One Relationship Represented with Attributes Containing Object Identifiers

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Systems Analysis and Design in a Changing World, 4th

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One-to-Many Relationship Between Customer and Order Classes

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Systems Analysis and Design in a Changing World, 4th Edition

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One-to-Many Relationship Represented with Attributes Containing Object Identifiers

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Many-to-Many Relationship Employee and Project Classes

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Generalization Hierarchy within

the RMO Class Diagram (Figure 12-21)

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Class diagram Example:

Example #1: Inheritance – Vehicles

This diagram shows an inheritance hierarchy – a series of classes and their subclasses. Its for an imaginary application that must model different kinds of vehicles such as bicycles, motor bike and cars.

Notes

 All Vehicles have some common attributes (speed and colour) and common behaviour (turnLeft, turnRight)

 Bicycle and MotorVehicle are both kinds of Vehicle and are therefore shown to inherit from Vehicle. To put this another way, Vehicle is the superclass of both Bicycle and MotorVehicle

 In our model MotorVehicles have engines and license plates. Attributes have been added accordingly, along with some behaviour that allows us to examine those attributes

 MotorVehicles is the base class of both MotorBike and Car, therefore these classes not only inherit the speed and colour properties from Vehicle, but also the additional attributes and behaviour from MotorVehicle

 Both MotorBike and Car have additional attributes and behaviour which arespecific to those kinds of object.

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Example #2: Mixed Example – Company, Employee, Manager

This example is from a system that models companies, e.g. for a payroll or reporting system. See if you can interpret it yourself!