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Software Engineering

Software Engineering (SE) is a professiondedicated to designing, implementing, andmodifying software so that it is of higher

quality, more affordable, maintainable, and

faster to build.

Systematic collection of past experience:

Techniques, Methodologies,

Guidelines.

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MODULE:I INTRODUCTION TO SOFTWARE

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The IEEE Definition

The IEEE Computer Society's Software Engineering

Body of Knowledge defines "software engineering"

as the application of a systematic, disciplined,

quantifiable approach to the development,

operation, and maintenance ofsoftware, and the

study of these approaches; that is, the application of

engineering to software.

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Why Study Software Engineering? (1)

To acquire skills to develop large programs

Exponential growth in complexity

and difficulty level with size.

The ad hoc approach breaks down

when size of software increases.

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Ability to solve complex programmingproblems:

How to break large projects into smallerand mana eable arts?

How to use abstraction?

Also learn techniques of:

Specification, design, user interfacedevelopment, testing, projectmanagement, etc.

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To acquire skills to be a better programmer:

- Higher Productivity

- Better Quality Programs

(Project Closure)

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PROGRAM vs SOFTWARE

PROGRAM

Usually small in size

Author himself is sole user

Single developer

SOFTWARE

Large

Large number of users

Team of developers

Lacks proper user interface

Lacks proper

documentation

Ad hoc development.

(Programmer Centric)

Well-designed interface

Well documented & user-

manual prepared

Systematic development

(Organization/Project

Centric)

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SOFTWARE

Software consists of three components:

-Program, when executed provides desired

function and performance.-Documents, t at escri e t e operation

and use of the program.

-Data structure, that enable the programs

to adequately manipulate information.

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Softwares Dual Role

Software is a product

Delivers computing potential

Produces, manages, acquires, modifies, displays, or

transmits information

Software is a vehicle for delivering a product

Supports or directly provides system functionality

Controls other programs (e.g., an operating system) Effects communications (e.g., networking software)

Helps build other software (e.g., software tools)

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Types of software:

1.System software

2.Application software/PC software

3.Engg. &scientific software.

5.Web based software

6.AI software

7.Embedded software

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System software : Managing and controlling operation ofcomputer system. It frequently interact with the hardware.

Ex-OS , assembler , compiler , linker , loader etc.

Application software : used for official and personal use on dailybasis and also to solve a particular business need.

Ex-MS word ,MS office , media player , power point etc.

: use or sc en c anengineering activities.

Ex-CAD, CAM , MATLAb (MATrix LABoratory)etc.

Real time software : observes , analyze and controls real worldevents as they occur. (Time Constraint is present)Ex- traffic light control.

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Web-based software : act as interface between userand internet .In other words it is used to develop web

based application.Ex-HTML , ASP , web browser etc.

AI software : used where the problem solving

technique is non algorithmic in nature.x- o ot cs , game p ay ng tec n que etc.

Embedded software : it is very small and embedded in

a small chip to perform limited application.Ex-automatic washing machine , s/w in DVD playeretc.


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Legacy Software

Whymustitchange? software must be adapted to meet the needs

of new computing environments or technology.

software must be enhanced to implement new.

software must be extended to make itinteroperable with other more modern

systems or databases. software must be re-architected to make it

viable within a network environment.

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Characteristics of software

1.Efficiency: the s/w must use the resource properly.

2.Maintainability: the s/w can change with a change withusers requirement.

3. On time: the s/w development must be within the.

4.Within the budget: the development cost of s/wshouldnt exceed budget specified by the client.

5.Functionality: it should meet all the functionalityspecified by the requirement.

6.Dependability: the s/w must be secured and reliable.


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Characteristics of software

1. Software is developed or engineered, it is

not manufactured in the classical sense.

2. software doesnt wear out.


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Failure curve of hardware


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Wear vs. Deterioration


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SE is a layered technology


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Generic view of s/w Engg.

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Emergence of SE

1. Early computer programming

2. High level language programming

3. Control flow based design

4. Structure oriented design

5. Data structure oriented design

6. Data flow oriented design

7. Object oriented design

8. Aspect orientation client-server design ,embedded s/w design.

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Early Computer Programming (50s)

Every programmer developed

his own style of writing(Coding,

documentation etc.) programs: ccor ng o s n u on an

in an ad hoc manner.

(exploratory programming).(build & fix)

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What is Wrong with the Exploratory

Style? Can successfully be used for very small

programs only.


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High-Level Language

Programming(Early 60s) High-level languages such as

FORTRAN, ALGOL, and COBOL wereintroduced:

efforts greatly.

Software development style was still

exploratory. Typical program sizes were limited to a

few thousands of lines of source code.


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Control Flow-Based Design

(late60s) Size and complexity of programsincreased further:

Exploratory programming style

Programmers found:

Very difficult to write cost

effective and correct programs.

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Control Flow-Based Design (late60s)

Programmers found: programs written by others very

difficult to understand and maintain.

To co e u with this roblem

experienced programmers advised:

``Pay particular attention to thedesign of the program's control

structure.'

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Control Flow-Based Design (late 60s)

A program's control structure

indicates:

The sequence in which the program'sinstructions are executed.

To help design programs having good

control structure: Flow charting technique was developed.


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Control Flow-Based Design (late 60s)

Using flow charting technique:

One can represent and design a program's

control structure. Usua y one un erstan s a program:

By mentally simulating the program's

execution sequence


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A program having a messy flow chart

representation:

Difficult to understand and debug


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It was found:

GO TO statements makes control

structure of a program messy. GO TO statements alter the flow of

control arbitrarily.

The need to restrict use of GO TOstatements was recognized.


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Many programmers had extensively used

assembly languages.

JUMP instructions are frequently usedor program ranc ng n assem y

languages.

Programmers considered use of GO TOstatements inevitable


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Control-flow Based Design (Late 60s)

At that time, Dijkstra published his

article:

Goto Statement Considered HarmfulComm. of ACM, 1969.

Many programmers were unhappy to read his

article.


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They published several counter articles:

Highlighting the advantages and

inevitability of GO TO statements


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But, soon it was conclusively proved:

Only three programming constructs are

sufficient to express any programminglogic:

sequence (e.g. a=0;b=5;)

selection (e.g. if(c=true) k=5 else m=5;) iteration (e.g. while(k>0) k=j-k;)


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Everyone accepted:

It is possible to solve any programming

problem without using GO TO statements. T s orme t e as s o Structure

Programming Methodology.


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Structured Programming

A program is called structured

When it uses only the following types of

constructs: sequence

selection

iteration


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Unstructured control flows are

avoided.

Consist of a neat set ofmodules.

Use single-entry, single-exit programconstructs.


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However, violations to this feature are

permitted:

Due to practical considerationssuc as:

Premature loop exit to support exception

handling.


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Structured programs are:

Easier to read and understand,

Easier to maintain, Require less effort and time for

development.


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Data Structure-Oriented Design

(Early70s) Soon it was discovered:

It is important to pay more attention to the

design of data structures of a program T an to t e es gn o ts contro structure.


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Data Structure-Oriented Design

(Early70s) Techniques which emphasize designing the

data structure:

Derive program structure from it:Are ca e ata structure or ente Des gn

techniques.


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Data Flow-Oriented Design (Late 70s)

Data flow-oriented techniques advocate:

The data items input to a system

must first be identified, Processing required on the data

items to produce the required

outputs should be determined.


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Data flow technique identifies:

Different processing stations (functions) in

a system. T e tems ata t at ow etween

processing stations.


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Data flow technique is a generic

technique:

Can be used to model the working ofany system.

not just software systems.

A major advantage of the data flowtechnique is its simplicity.


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Object-Oriented Design (80s)

Object-oriented technique:

An intuitively appealing design

approach: Natural objects (such as employees,

pay-roll-register, etc.) occurring in

a problem are first identified.


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Relationships among objects:

Such as composition, reference,

and inheritance are determined. Each object essentially acts as

A data hiding (or data abstraction)

entity.


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Object-Oriented Techniques have gained wide

acceptance:

Simplicity

Reuse poss t es

Lower development time and cost

More robust code

Easy maintenance


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Evolution of design techniques


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Software Crisis

Software products:

Fail to meet user requirements.

Frequently crash. Expensive.

Difficult to alter, debug, and enhance.

Often delivered late. Use resources non-optimally


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Software Crisis (cont.)


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Factors Contributing to the Software

Crisis Larger problems

Lack of adequate training in software

engineering

Increas ng s s ortage

Low productivity improvements.


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Types of Software Projects

Software products Outsourced projects


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Reference

Fundamentals of Software Engineering,

Prentice-Hall of India, By R.Mall CHAPTER -1.

Software Engineering: A Practitioners

, , . . , ,

CHAPTER-1.


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