We live in a world of objects. These objects exist in nature, in man-made
entities,
in business, and in the products that we use. They can be categorized, described,
organized, combined, manipulated and created. Therefore, an
object-oriented
view has come into picture for creation of computer software. An
object-oriented
approach to the development of software was proposed in late 1960s.
Object-Oriented
development requires that object-oriented techniques be used during the analysis,
and implementation of the system. This methodology asks the analyst to determine
what the objects of the system are, how they behave over time or in response to
events, and what responsibilities and relationships an object has to other objects.
Object-oriented analysis has the analyst look at all the objects in a system,
their commonalties, difference, and how the system needs to manipulate the objects.
Object Oriented Process
The Object Oriented Methodology of Building
Systems takes the objects as the basis. For this, first the system to be developed
is observed and analyzed and the requirements are defined as in any other method
of system
development. Once this is done, the objects in the required system are identified.
For example in case of a Banking System, a customer is an object, a chequebook
is an object, and even an account is an object.
In simple terms, Object Modeling is based on identifying the objects in a system
and their interrelationships. Once this is done, the coding
of the system is done. Object Modeling is somewhat similar to the traditional
approach of system designing, in that it also follows a sequential process of
system
designing but with a different approach. The basic steps of system designing
using Object Modeling may be listed as:
System Analysis
As in any other system development model, system
analysis is the first phase of development in case of Object
Modeling too. In this phase, the developer interacts with the user of the
system to find out the user requirements and analyses the system to understand
the functioning.
Based on this system study, the analyst prepares a model of the desired system.
This model is purely based on what the system is required to do. At this stage
the implementation details are not taken care of. Only the model of the system
is prepared based on the idea that the system is made up of a set of interacting
objects. The important elements of the system are emphasized.
System Design
System
Design is the next development stage where the overall architecture of the
desired system is decided. The system is organized as a set of sub systems interacting
with each other. While designing the system as a set of interacting subsystems,
the analyst takes care of specifications as observed in system analysis as well
as what is required out of the new system by the end user.
As the basic philosophy
of Object-Oriented method of system
analysis is to perceive the system as a set of interacting objects, a bigger
system may also be seen as a set of interacting smaller subsystems that in turn
are composed of a set of interacting objects. While designing the system, the
stress lies on the objects comprising the system and not on the processes being
carried out in the system as in the case of traditional Waterfall Model where
the processes form the important part of the system.
Object Design
In this phase, the details of the system analysis and system design are implemented.
The Objects identified in the system design phase are designed. Here the implementation
of these objects is decided as the data structures get defined and also the interrelationships
between the objects are defined.
Let us here deviate slightly from the design process and understand first a
few important terms used in the Object-Oriented
Modeling.
As already discussed, Object
Oriented Philosophy
is very much similar to real world and hence is gaining popularity as the systems
here are seen as a set of interacting objects as in the real world. To implement
this concept, the process-based structural programming is not used; instead objects
are created using data structures. Just as every programming
language provides various data types and various variables of that type can
be created, similarly, in case of objects certain data types are predefined.
For example, we can define a data type called pen and then create and use several
objects of this data type. This concept is known as creating a class.
Class: A class is a collection of similar objects. It is a
template where certain basic characteristics of a set of objects are defined.
The class defines the basic attributes and the operations of the objects of that
type. 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 created as per the
requirement of the case.
Abstraction: Classes are built on the basis of abstraction,
where a set of similar objects are observed and their common characteristics are
listed. Of all these, the characteristics of concern to the system under observation
are picked up and the class definition is made. The attributes of no concern to
the system are left out. This is known as abstraction.
The abstraction of an object varies according to its application. For instance,
while defining a pen class for a stationery shop, the attributes of concern might
be the pen color, ink color, pen type etc., whereas a pen class for a manufacturing
firm would be containing the other dimensions of the pen like its diameter, its
shape and size etc.
Inheritance: Inheritance is another important concept in this
regard. This concept is used to apply the idea of reusability of the objects.
A new type of class can be defined using a similar existing class with a few new
features. For instance, a class vehicle can be defined with the basic functionality
of any vehicle and a new class called car can be derived out of it with a few
modifications. This would save the developers time and effort as the classes already
existing are reused without much change.
Coming back to our development process, in the Object Designing phase of the
Development process, the designer decides onto the classes in the system based
on these concepts. The designer also decides on whether the classes need to be
created from scratch or any existing classes can be used as it is or new classes
can be inherited from them.
Implementation
During this phase, the class objects and the interrelationships of these classes
are translated and actually coded using the programming
language decided upon. The databases
are made and the complete system is given a functional shape.
The complete OO methodology revolves around the objects identified in the system.
When observed closely, every object exhibits some characteristics and behavior.
The objects recognize and respond to certain events. For example, considering
a Window on the screen as an object, the size of the window gets changed when
resize button of the window is clicked.
Here the clicking of the button is an event to which the window responds by
changing its state from the old size to the new size. While developing
systems based on this approach, the analyst makes use of certain models to
analyze and depict these objects. The methodology supports and uses three basic
Models:
-
Object Model - This model describes the objects in a system
and their interrelationships. This model observes all the objects as static and
does not pay any attention to their dynamic nature.
-
Dynamic Model - This model depicts the dynamic aspects of
the system. It portrays the changes occurring in the states of various objects
with the events that might occur in the system.
-
Functional Model - This model basically describes the data
transformations of the system. This describes the flow of data and the changes
that occur to the data throughout the system.
While the Object Model is most important of all as it describes the basic element
of the system, the objects, all the three models together describe the complete
functional system.
As compared to the conventional system development techniques, OO modeling
provides many benefits. Among other benefits, there are all the benefits of using
the Object Orientation. Some of these are:
-
Reusability - The classes once defined can easily be used by other applications.
This is achieved by defining classes and putting them into a library of classes
where all the classes are maintained for future use. Whenever a new class is needed
the programmer looks into the library of classes and if it is available, it can
be picked up directly from there.
-
Inheritance - The concept of inheritance helps the programmer use the existing
code in another way, where making small additions to the existing classes can
quickly create new classes.
-
Programmer has to spend less time and effort and can concentrate on other aspects
of the system due to the reusability feature of the methodology.
-
Data Hiding - Encapsulation is a technique that allows the programmer to hide
the internal functioning of the objects from the users of the objects. Encapsulation
separates the internal functioning of the object from the external functioning
thus providing the user flexibility to change the external behaviour of the object
making the programmer code safe against the changes made by the user.
-
The systems designed using this approach are closer to the real world as the
real world functioning of the system is directly mapped into the system designed
using this approach.
Advantages of Object Oriented Methodology
-
Object Oriented Methodology closely represents the problem domain. Because
of this, it is easier to produce and understand designs.
-
The objects in the system are immune to requirement changes. Therefore, allows
changes more easily.
-
Object Oriented Methodology designs encourage more re-use. New applications
can use the existing modules, thereby reduces the development cost and cycle time.
-
Object Oriented Methodology approach is more natural. It provides nice structures
for thinking and abstracting and leads to modular design.
