Characteristics of commercial Software• Developed for some clients under formal contracts• Software is designed based on some specification• Developed in teams and not by individuals• Includes detailed documentation• Meant for users• Requires some modification from time to time.• Requires some modification from time to time.• Does not wear out but has a lifespan, after which it becomes
obsolete.• Software failure may create catastrophe. So software is designed
for utmost reliability.• A computer system is prone to misuse or sabotage. So software
Software DevelopmentDesign and development of software requires great amount ofeffort, time and money
Computer programming is just one part of the process.
It requires a systematic approach that includes• Comprehensive methods• Tools for efficient execution of methods• Procedures for quality assurance• Coordination and control
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• Coordination and controlIt also involves people and their management.
All these engineering aspects relating to software developmenthave combined together to evolve as a disciplinecalled Software Engineering.
Software CrisisDuring 1970s, large numbers of software projects failed mostlydue to human factors. This problem was referred to as the“software crisis”.
Study by Comptroller General of the United States (1979): 2% of software worked on delivery3% worked only after some corrections45% delivered, but never successfully used20% used, only after major modification/ reworked20% used, only after major modification/ reworked30% were paid for, never completed/ delivered
Software Crisis led to Software Engineering
Software Engineering• Systematic approach to software development• Application of engineering principles• Provides a set of methods, tools, and procedures• Ensures consistent software quality
Software Processrefers to methods of developing software
It has four major component processes1. Software Development Process2. Software Project Management Process3. SoftwareConfigurationManagementProcess3. SoftwareConfigurationManagementProcess4. Software Process Management Process
Software Development ProcessIt is a structured set of activities that transformthe userrequirements into a quality software product.
The Waterfall modelTraditional sequential process modelSoftware development takes place in well defined phases
1. System Engineering2. Requirement Analysis3. Design
4. Implementation or Coding5. Verification or testing6. Maintenance
TheV-modelExtension of Waterfall modelStipulates various kinds of testing, like unit (module) testing andintegration testing.Information from earlier phases also used for testing
Evolutionary prototypingInitial working model of software basedon outline specification. This prototypeis evaluated and refined in number ofstagesto getfinal product.stagesto getfinal product.
Spiral model: Each cycle consists of four step
1. Planning 2. Risk Analysis 3. Engineering 4. ValidationSpiral model emphasizes on risk management.
Iterative Waterfall Model: It overcomes the limitations of
Waterfall Model by adding an “iterative” loop. After end of each phase, itsprevious phases are revisited to modify requirements and to remove errors.
1.1 Name & purpose of software; 1.2 Scope, benefits, objectives, and goals; 1.3 Typesof audience/ users
2. Overall Description
2.1 Product Perspective: Context and origin (how initiated?); Block diagram of overallsystem to which software relates; 2.2 Product Features: Major features and significantfunctions; Organization of functions/ modules; 2.3 Category/ types of users; 2.4Performance Requirements; 2.5 Operating Environment: Hardware platform, operatingsystem, database system, etc.; 2.6 Design and Implementation Constraints; 2.7 Security,safety and privacy Requirements; 2.8 User Documentation; 2.9 Assumptions
Approaches to Software EngineeringSystem for which software is to be developed is successively broken down (decomposed) into parts and arranged in to hierarchy.
Decomposition is a convenient way of handling any complex problem. complex problem.
Function Oriented ApproachFO approach is traditional. It supports structuredprogrammingA structured programconsists of functions (modules) organized in ahierarchy.
Higher level function invokes lower level function.Data is either local or global
Steps of OOA•Define User Viewof Requirements•Identify Analysis Objects and their Characteristics•Determine Object Dynamics•Determine Object Interactions and relationship
Diagrams used in OOA.Use case diagram Describes how users interact with processes
Class diagram It is used to refine the use case diagram and define a
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Class diagram It is used to refine the use case diagram and define adetailed design of the system
State diagram Represents different states that objects in the systemundergo during their life cycle
Activity diagram Describes the process flow of the system
Sequence diagram Represents interaction between objects
Collaboration diagram Groups together interactions between objects.
Fundamental questions in OOD•What objects do we need?•What behaviours are required?•How do we distribute behaviour over the set of objects?
Classes, Attributes, Methods and Associations
Static Modelling’
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Designed for implementation in OOD
Identified in OOA
Objects also performsome action. Defining thebehaviour (methods) of objects is called the‘Dynamic Modelling’.
– Understand the problem– Specify requirements (WHAT)– Design the solution (HOW)– Write the code– Test and deploy
Similar types of tasks
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Similar types of tasks – Elicitation of requirements – Documentation of requirements– Identification of software modules– Design of software modules– Acceptance tests
Similar project management issues e.g. Planning, Estimating, Monitoring & Control, Communicating
How OO Approach is different?• Different View of the System• Integration of Data and Method• Different Documentation Tools• Real World Focus• Approach to Project Life Cycle• Approachto ProgramCoding
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• Approachto ProgramCoding• Approach to Component Reuse• Approach to Software Maintenance
FO methodology is more suitable for data intensive softwareprojects, whereas OO methodology is more suitable forsoftware project that requires complex algorithm/ processinglogic.
