Page 32 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Object Oriented Analysis and Design

Notes objects. You can say that object oriented development is an indirect way of system development
because in this approach a holistic view of application domain is considered, and objects are
identified in the related problem domain. A historic view of application helps in realizing the
situations and characteristics of the system. Taking a holistic view of the problem domain rather
than considering functional requirements of a single problem give an edge to object oriented
development. Once the objects are created with the needed characteristics, they communicate
with each other by message passing during problem solving.

3.1 Object and Class Concepts

3.1.1 Class

A class is a collection of things, or concepts that have the same characteristics. Each of these
things or concepts is called an object. Classes define the basic words of the system being modeled.
A class describes a collection of similar objects. It is a template where certain basic characteristics
of a set of objects are defined. A class defines the basic attributes and the operations of the objects
of that type. Using a set of classes as the core vocabulary of a software project tends to greatly
facilitate understanding and agreement about the meanings of terms, and other characteristics
of the objects in the system.
Classes can serve as the foundation for data modeling. In OOM, the term classes is usually the
base from which visual modeling tools such as Rational Rose XDE, Visual Paradigm function
and design the model of systems.
Defining a class does not define any object, but it only creates a template. For objects to be
actually created, instances of the class are to be created as per the requirement of the case. Now,
let us see how the characteristics that classes are captured as attributes and operations. These
terms are defined as follows:
Attributes are named slots for data values that belong to the class

Operations represent services that an object can request to affect the behaviour of the
object or the system itself.

Did u know? Different objects of a given class typically have at least some differences in
the values of their attributes.
The notation for a class is a box with three sections. The top section contains the name of the class
in boldface type, the middle section contains the attributes that belong to the class, and the
bottom section contains the class’s operations as you can see in Figure 3.1.
Figure 3.1: Class notation

Class

Attributes

Operations

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