Page 57 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Anil Sharma, Lovely Professional University
Unit 5: Advanced Class Modelling – II

Unit 5: Advanced Class Modelling – II Notes

CONTENTS
Objectives

Introduction
5.1 Abstract Classes
5.2 Constraints

5.3 Derived Data
5.4 Packages
5.4.1 Logical Horizon
5.5 Summary

5.6 Keywords
5.7 Review Questions

5.8 Further Readings
Objectives

After studying this unit, you will be able to:
Explain the concept of Abstract Classes
Discuss Constraints

Discuss the concept of Derived Data
Explain Packages

Introduction

In the previous unit, we have discussed advanced object and class concepts, concept of association
ends, N-ary associations, concept of aggregation, and different types of aggregation. In this unit,
we will discuss some other advanced aspects of object modeling which are required to model
complex and large applications. We will discuss the concept of abstract classes, constraints,
derived data, and packages. In packages, we will discuss the concept of logical horizon and
various examples of packages.

5.1 Abstract Classes

An abstract class is a class that has no direct instances. The descendant classes can also be abstract,
but the generalization hierarchy must ultimately terminate in subclasses with direct instances.

Example: In Figure 5.1 Person is an abstract class but the subclasses Manager and
Individual Contributor are concrete.

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