Software Design

Introduction

• Software Design helps developers to develop and implement the user requirements in the form of software.
• There are different types of software design
  • Architechtural Design:
    • Shows relationship between major modules.
    • Finalizes on the design pattern to be used.
  • Design Design: Focuses on the data structure representation
  • Interface Design: Shows the flow of the information
  • Component Design: provides a higher level of abstraction and divides the problem into sub-problems, each associated with component partitions

Software Designing strategy

• Good software design will have the following features
  • Abstraction
  • Highly cohesive modules
  • Loosely coupled modules
  • Partitionaed
  • Maintability and
  • possibility of the forward engineering
• Coupling and Cohesion
  • Coupling: is the degree of interdependencies between modules
  • Cohesion: cohesion measures the strength of relationship between pieces of functionality within a given module
  • A good design will be loosely coupled and tight cohesion
  • A focused class which performs its own responsibility is considered highly cohesive class. In contrast, suppose you are using 2 independent classes. Change in one class requires change in another class. This is considered that both the classes are tightly coupled.
• Abstraction
  • Suppose there are two projects managed by one project manager. The team under him has two leads and developers under leads. Each lead manages one project each. If we build a system then there will be following level of abstractions\
    • Project manager can see information of 2 projects. He can also see employee information as well.
    • Leads can see th project where he is assigned.

Partitioning in Software design

• A program structure can be divided into both horizontally and vertically
• A system can be broken down into subsystems.
  • There could be some processes common among the sub systems. In horizontal partitioning these common processes connect all sub-systems. With horizontal partitioning thought is given to the whole at design time.
  • In case of vertical partitioning there is no connection between the individual sub systems. Below image shows vertical and horizontal partitioning
    

Forward Engineering vs Reverse Engineering

• Forward engineering refers to taking a high-level model and using it to build a more complex lower-level implementation. Example Write java classes from UML class diagram.
• Reverse engineering takes a complex implementation and try and convert it into a higher level abstraction. Example Create UML diagram from implementated java classes.

State transition diagram

• State transition diagram describes the behavior of a single object in response to a series of events in a system
• The difference between flowchart and state transition diagram is - Flow chart shows the processes that changes the state of an object but does not show what state change has happened in the object
• States are used to represent the behavior models of a single object
• State of a object changes when any action or pre conditions get applied on it

Below is an example of the state diagram