What is Object-Oriented Analysis?

1.8.3.1 Object-Oriented Analysis (OOA)

Object-oriented analysis helps to create a precise and concise model of the problem in terms of real world objects. A system can be broken into many small objects. An application can be developed by assembling all these objects together. Object-oriented systems help to develop software applications that can be easily reused, modified and maintained.

Object-oriented analysis is based on the following concepts:

·         Objects: An object is an entity or thing that has certain characteristics such as table, chair, car etc

·         Classes: A class is the general category to which objects belong. Furniture is a class and table and chair objects belong to this class

·         Inheritance: The child class derived from parent class inherits the characteristics and functions of the parent class

·         Encapsulation: Encapsulation is putting together all the operations that can be performed on an object along with its definition.

·         Polymorphism: It is the ability of a function to exist in more than one form.

Models based on OOA serve as model for creating software systems. UML (Unified Modeling Language) is the standard modeling language for object-oriented development. It is used to draw different types of visual diagrams to represent various aspects of the system.

The following figure illustrates the use of UML diagrams used to model cash withdrawal from a savings account system.

1.8.3.2 Structured Analysis

Structured Analysis is a set of techniques and graphical tools used to develop system specifications. The analysis model must achieve three primary objectives:

·         Describe what customer requires

·         Establish a basis for the creation of software design

·         Define the set of requirements that can be validated once the software is built

Structured Analysis is a traditional approach that represents information and data as flowcharts. The whole system is viewed as one large activity with inputs arriving from sources and outputs leaving it. It uses three main tools in the requirements analysis phase.

1.8.3.3 Data Flow Diagrams

A data-flow diagram is a pictorial representation of a system’s functions. Functions form part of various processes that are executed for a system. A data-flow diagram depicts the interaction of the processes, the data used by the processes and the transformation of data during processing.

Context diagrams are also used to represent and depict a system. A DFD is a more detailed representation of the system. A  Context diagram only deals with boundary of the system. It represents the software model as a single and large process with input and output data. It is displayed by incoming and outgoing arrows respectively. It focuses on the main data-flow in a system. It establishes the relationships between external entities of system and the system via the data (flows) that they exchange. To enable a DFD to start from a context diagram, single bubble of the context diagram is partitioned into more bubbles to reveal the details of processing in the system.

The data-flow diagrams are basically process-oriented. They are used to model the functions performed by a system.

1.8.3.4 Entity Relationship Diagram

Another graphical tool Entity Relationship Diagram (ERD) is used to model the stored data layout of the system. It is purely data-oriented modeling process. An entity relationship diagram illustrates data t rest. Data-flow diagrams illustrate the data in motion.

An entity is anything about which information is stored. ERD focuses on relationship of data structures with one another. It identifies a relationship and gives it a name.

ERDs are important because of the following reasons:

·         Users emphasize more on data than processes. This is because data can be seen and read and many users are comfortable with it. But processes are abstract and cannot be seen or read. So the users cannot immediately identify them.

·         They help in identifying keys and indexes for accessing data in a system.

·         They establish relationships among data structures.

ERD diagram has become an essential tool for database modeling. It helps to draw a picture of data that describes the objects in database (entities or tables) and how they relate to one another. It helps to identify the facts about the important objects (attributes or fields).

The following figure illustrates the use of ERD to model a “Movies Database” with all its entities and their attributes.