Object Oriented Analysis and Design

Object Oriented Analysis & Design Tutorial

Object–Oriented Analysis (OOA) is the procedure of identifying software engineering requirements and developing software specifications in terms of a software system’s object model, which comprises of interacting objects. This tutorial will help you understand the basics of object-oriented analysis and design along with its associated terminologies.

Audience

This tutorial has been designed to help beginners. After completing this tutorial, you will find yourself at a moderate level of expertise from where you can take yourself to next levels.

Prerequisites

Before you start proceeding with this tutorial, it is assumed that you have basic understanding of computer programming and related programming paradigms…………Read More

OOAD – Object Model

The object model visualizes the elements in a software application in terms of objects. In this chapter, we will look into the basic concepts and terminologies of object–oriented systems.

Objects and Classes

The concepts of objects and classes are intrinsically linked with each other and form the foundation of object–oriented paradigm.

Object

An object is a real-world element in an object–oriented environment that may have a physical or a conceptual existence. Each object has:

• Identity that distinguishes it from other objects in the system.
• State that determines the characteristic properties of an object as well as the values of the properties that the object holds.
• Behavior that represents externally visible activities performed by an object in terms of changes in its state…….Read More

Object Oriented System

We know that the Object-Oriented Modelling (OOM) technique visualizes things in an application by using models organized around objects. Any software development approach goes through the following stages:

• Analysis,
• Design, and
• Implementation.

In object-oriented software engineering, the software developer identifies and organizes the application in terms of object-oriented concepts, prior to their final representation in any specific programming language or software tools.

Phases in Object-Oriented Software Development

The major phases of software development using object–oriented methodology are object-oriented analysis, object-oriented design, and object-oriented implementation.

Object–Oriented Analysis

In this stage, the problem is formulated, user requirements are identified, and then a model is built based upon real–world objects. The analysis produces models on how the desired system should function and how it must be developed. The models do not include any implementation details so that it can be understood and examined by any non–technical application expert……Read More

Object Oriented Principles

Principles of Object-Oriented Systems

The conceptual framework of object–oriented systems is based upon the object model. There are two categories of elements in an object-oriented system:

Major Elements : By major, it is meant that if a model does not have any one of these elements, it ceases to be object oriented. The four major elements are:

• Abstraction
• Encapsulation
• Modularity
• Hierarchy

Minor Elements : By minor, it is meant that these elements are useful, but not indispensable part of the object model. The three minor elements are:

• Typing
• Concurrency
• Persistence……….Read More

Object Oriented Analysis

In the system analysis or object-oriented analysis phase of software development, the system requirements are determined, the classes are identified and the relationships among classes are identified.

The three analysis techniques that are used in conjunction with each other for object-oriented analysis are object modelling, dynamic modelling, and functional modelling.

Object Modelling

Object modelling develops the static structure of the software system in terms of objects. It identifies the objects, the classes into which the objects can be grouped into and the relationships between the objects. It also identifies the main attributes and operations that characterize each class.

The process of object modelling can be visualized in the following steps:

• Identify objects and group into classes
• Identify the relationships among classes
• Create user object model diagram
• Define user object attributes
• Define the operations that should be performed on the classes
• Review glossary……..Read More

Dynamic Modelling

The dynamic model represents the time–dependent aspects of a system. It is concerned with the temporal changes in the states of the objects in a system. The main concepts are:

• State, which is the situation at a particular condition during the lifetime of an object.
• Transition, a change in the state
• Event, an occurrence that triggers transitions

Action, an uninterrupted and atomic computation that occurs due to some event, and

• Concurrency of transitions.

A state machine models the behavior of an object as it passes through a number of states in its lifetime due to some events as well as the actions occurring due to the events. A state machine is graphically represented through a state transition diagram……..Read More

Functional Modelling

Functional Modelling gives the process perspective of the object-oriented analysis model and an overview of what the system is supposed to do. It defines the function of the internal processes in the system with the aid of Data Flow Diagrams (DFDs). It depicts the functional derivation of the data values without indicating how they are derived when they are computed, or why they need to be computed.

Data Flow Diagrams

Functional Modelling is represented through a hierarchy of DFDs. The DFD is a graphical representation of a system that shows the inputs to the system, the processing upon the inputs, the outputs of the system as well as the internal data stores. DFDs illustrate the series of transformations or computations performed on the objects or the system, and the external controls and objects that affect the transformation.

Rumbaugh et al. have defined DFD as, “A data flow diagram is a graph which shows the flow of data values from their sources in objects through processes that transform them to their destinations on other objects.”

The four main parts of a DFD are:…..Read More

UML Analysis Model

The Unified Modeling Language (UML) is a graphical language for OOAD that gives a standard way to write a software system’s blueprint. It helps to visualize, specify, construct, and document the artifacts of an object-oriented system. It is used to depict the structures and the relationships in a complex system.

Brief History

It was developed in 1990s as an amalgamation of several techniques, prominently OOAD technique by Grady Booch, OMT (Object Modeling Technique) by James Rumbaugh, and OOSE (Object Oriented Software Engineering) by Ivar Jacobson. UML attempted to standardize semantic models, syntactic notations, and diagrams of OOAD.

Systems and Models in UML

System : A set of elements organized to achieve certain objectives form a system. Systems are often divided into subsystems and described by a set of models.

Model : Model is a simplified, complete, and consistent abstraction of a system, created for better understanding of the system……..Read More

UML Basic Notations

UML defines specific notations for each of the building blocks.

Class

A class is represented by a rectangle having three sections:

• the top section containing the name of the class
• the middle section containing class attributes
• the bottom section representing operations of the class

The visibility of the attributes and operations can be represented in the following ways:…..Read More

UML Structured Diagrams

UML structural diagrams are categorized as follows: class diagram, object diagram, component diagram, and deployment diagram.

Class Diagram

A class diagram models the static view of a system. It comprises of the classes, interfaces, and collaborations of a system; and the relationships between them.

Class Diagram of a System

Let us consider a simplified Banking System.

A bank has many branches. In each zone, one branch is designated as the zonal head office that supervises the other branches in that zone. Each branch can have multiple accounts and loans. An account may be either a savings account or a current account. A customer may open both a savings account and a current account. However, a customer must not have more than one savings account or current account. A customer may also procure loans from the bank.

The following figure shows the corresponding class diagram……Read More

UML Behavioural Diagrams

UML behavioral diagrams visualize, specify, construct, and document the dynamic aspects of a system. The behavioral diagrams are categorized as follows: use case diagrams, interaction diagrams, state–chart diagrams, and activity diagrams.

Use Case Model

(a) Use case

A use case describes the sequence of actions a system performs yielding visible results. It shows the interaction of things outside the system with the system itself. Use cases may be applied to the whole system as well as a part of the system.

(b) Actor

An actor represents the roles that the users of the use cases play. An actor may be a person (e.g. student, customer), a device (e.g. workstation), or another system (e.g. bank, institution).

The following figure shows the notations of an actor named Student and a use case called Generate Performance Report………Read More

Object Oriented Design

After the analysis phase, the conceptual model is developed further into an object-oriented model using object-oriented design (OOD). In OOD, the technology-independent concepts in the analysis model are mapped onto implementing classes, constraints are identified, and interfaces are designed, resulting in a model for the solution domain. In a nutshell, a detailed description is constructed specifying how the system is to be built on concrete technologies

The stages for object–oriented design can be identified as:

• Definition of the context of the system
• Designing system architecture
• Identification of the objects in the system
• Construction of design models
• Specification of object interfaces

Object-Oriented System Design

System Design

Object-oriented system design involves defining the context of a system followed by designing the architecture of the system……Read More

OOAD Implementation Strategies

Implementing an object-oriented design generally involves using a standard object oriented programming language (OOPL) or mapping object designs to databases. In most cases, it involves both.

Implementation using Programming Languages

Usually, the task of transforming an object design into code is a straightforward process. Any object-oriented programming language like C++, Java, Smalltalk, C# and Python, includes provision for representing classes. In this chapter, we exemplify the concept using C++.

The following figure shows the representation of the class Circle using C++.

………Read More

OOAD Testing and Quality Assurance

Once a program code is written, it must be tested to detect and subsequently handle all errors in it. A number of schemes are used for testing purposes.

Another important aspect is the fitness of purpose of a program that ascertains whether the program serves the purpose which it aims for. The fitness defines the software quality.

Testing Object-Oriented Systems

Testing is a continuous activity during software development. In object-oriented systems, testing encompasses three levels, namely, unit testing, subsystem testing, and system testing.

Unit Testing

In unit testing, the individual classes are tested. It is seen whether the class attributes are implemented as per design and whether the methods and the interfaces are error-free. Unit testing is the responsibility of the application engineer who implements the structure.

Subsystem Testing

This involves testing a particular module or a subsystem a………Read More