Software Engineering | Function Oriented and Object-Oriented Design

There are two fundamentally different approaches to software design that are in use today: function-oriented design and object oriented design. The object-oriented approach is a relatively newer technology and is still evolving. For development of large programs, the object-oriented approach is becoming increasingly popular due to certain advantages that it offers. On the other hand, function-oriented designing is a mature technology and has a large following.

Function-Oriented Design:

Function Oriented Design is an approach to software design where the design is decomposed into a set of interacting units or modules where each unit or module has a clearly defined function. Basically, the system is designed from a functional viewpoint.

A function oriented design strategy relies on decomposing the system into a set of interacting functions with a centralized system state shared by these functions.

In function-oriented design approach, the system is comprised of many smaller sub-systems known as functions. These functions are capable of performing significant task in the system.

This design mechanism divides the whole system into smaller functions, which provides means of abstraction by concealing the information and their operation.. These functional modules can share information among themselves by means of information passing and using information available globally.

Generic Procedure:

• Start with a high level description of what the software / program does.
• Refine each part of the description one by one by specifying in greater details the functionality of each part.
• These points lead to Top-Down Structure

Function-Oriented Design Strategies:

The following strategies are used to implement Function-Oriented Design:

Data Flow Diagram (DFD):

Data flow diagram is graphical representation of flow of data in an information system. Data-flow design is concerned with designing a series of functional transformations that convert system inputs into the required outputs. The design is described as data-flow diagrams. These diagrams show how data flows through a system and how the output is derived from the input through a series of functional transformations. Data-flow diagrams are a useful and intuitive way of describing a system.

Data Dictionaries:

Data dictionaries are simply repositories to store information about all data items defined in DFDs. A data dictionary lists all data elements appearing in the DFD model of a system. The data items listed contain all data flows and the contents of all data stores looking on the DFDs in the DFD model of a system.

A data dictionary lists the objective of all data items and the definition of all composite data elements in terms of their component data items.

Structure Charts:

Structure chart is a chart derived from Data Flow Diagram. It represents the system in more detail than DFD. It breaks down the entire system into lowest functional modules, describes functions and sub functions of each module of the system to a greater detail than DFD. Structure chart represents hierarchical structure of modules. At each layer a specific task is performed.

Pseudo-code:

Pseudo-code notations can be used in both the preliminary and detailed design phases. Using pseudo-code, the designer describes system characteristics using short, concise, English Language phases that are structured by keywords such as If-Then-Else, While-Do, and End.

Object-Oriented Design:

Object-oriented design (OOD) is an approach to software design that uses a process of defining objects and their interactions when planning code to develop software. In object oriented design approach, instead of concentrating on function, we concentrate upon objects. An object contains both data and function which are used to create applications.

OOD approach is mainly the process of using an object methodology to design a computing system or application. This technique enables the implementation of a software solution based on the concepts of objects.

An object-oriented design process involves designing the object classes and the relationships between these classes. In the object-oriented design approach, a system is viewed as a collection of objects (i.e., entities). Each object has its own state and behavior.

Concepts of Object Oriented Design:

The important concepts of Object Oriented Design:

Objects: All entities involved in the solution design are known as objects. For example, person, banks, company and customers are treated as objects. Every entity has some attributes associated to it and has some methods to perform on the attributes.

Classes: A class is a generalized description of an object. An object is an instance of a class. Class defines all the attributes, which an object can have and methods, which defines the functionality of the object.

Messages: Objects communicate via messages. Messages are implemented as procedure or function calls.
Abstraction: It is used for handling complexity. Removes irrelevant data and shows only essential data.

Encapsulation: It is the concept of information hiding. In OOD, the attributes (data variables) and methods (operation on the data) are bundled together is called encapsulation. Encapsulation not only bundles important information of an object together, but also restricts access of the data and methods from the outside world. This is called information hiding.

Inheritance: This is the ability of a class to extend or override the functionality of another class. OOD allows similar classes to stack up in hierarchical manner where the lower or sub-classes can import, implement and re-use allowed variables and methods from their immediate super classes. This property of OOD is known as inheritance. This makes it easier to define specific class and to create generalized classes from specific ones.

Polymorphism: This is the ability to define different functions or classes as having the same name, but taking different data type. OOD languages provide a mechanism where methods performing similar tasks but vary in arguments, can be assigned same name. This is called polymorphism, which allows a single interface performing tasks for different types. Depending upon how the function is invoked, respective portion of the code gets executed.