Page 42 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Object Oriented Analysis and Design

Notes 3.5 Summary

A class describes a collection of similar objects. It is a template where certain basic
characteristics of a set of objects are defined.

The notation for an object is the same in basic form as that for a class.
Objects usually appear as components of a larger program or a system. Through the
interaction of these objects, functionality of systems is achieved.

Links and associations are the basic means used for establishing relationships among
objects and classes of the system.

Association and classes are similar in the sense that classes describe objects, and association
describes links.
Multiplicity in an association specifies how many objects participate in a relationship.
Multiplicity decides the number of related objects.
Generalization is the relationship between a class, and it defines a hierarchy of abstraction
in which subclasses (one or more) inherit from one or more superclasses.
Generalization is used to refer to the relationship among classes, and inheritance is used
for sharing attributes and operations using the generalization relationship.

3.6 Keywords

Association: Association defines a relationship between two or more classes that specifies
connections among their instances.
Attributes: Attributes are named slots for data values that belong to the class.

Class: Class is a template where certain basic characteristics of a set of objects are defined.
Generalization: Generalization is the relationship between a class, and it defines a hierarchy of
abstraction in which subclasses (one or more) inherit from one or more superclasses.

Inheritance: Inheritance is a relationship between classes where one class is the parent class of
another (derived) class.
Link: A link is a physical or conceptual connection between objects.

Multiplicity: Multiplicity in an association specifies how many objects participate in a
relationship.
Object: An object is anything, real or abstract, about which we store data and those methods that
manipulate the data.

3.7 Review Questions

1. What is a class? Make distinction between attributes and operations.
2. Describe the differences between the notations of class and object respectively.

3. Illustrate the concept of objects and classes with examples.
4. Explain the concept of communication by message passing. Also discuss the advantages of
message passing.

5. Elucidate the concept of link and association with example.

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