2Basic Concepts

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November 8, 2011 Software Engineering, 2nd Sem. 2011-12

Software EngineeringBasic Concepts

Mrs. Ma. Christina FlorentinoMrs. Ma. Christina Florentino

CITE FacultyCITE Faculty

Sources: 1. Software Engineering & Testing by Agarwal, Tayal, Gupta

2. Software Engineering by Pressman


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Introduction to Software

Definition:

It is a set of instructions used to

Acquire inputs

Manipulate inputs to produce output

Includes:

Instructions

Data Structures

Documents that describes the operation and use of theprograms

IEEE: It is a collection of computer programs,

procedure rules and associated documentation

and data


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Importance of Software

It is the engine that drives business

decision making

Serves as the basis for modern

scientific investigation and engineering

problem-solving

Embedded in all kinds of systems


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Types of Software

2 Categories:

1. System Software. OS and all utilities

that enables the computer the function

2. Application Software. Programs that do

real work for users.


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Classes of Software

1. Generic Software. Designed forbroad customer market whose

requirements are very common, fairlystable and well understood by thesoftware engineer.

- sold in the open market

- there could be several competitorsin the market


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Classes of Software

2. Customized Software. Developed

for a customer where domain,

environment and requirements are

unique to that customer and cannot

be satisfied by generic products


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Generic vs. Customized

Developer manages Generic products;

customer manages customized

product

Requirements and specifications of a

generic product is controlled by the

developer


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Introduction to Software Engineering

IEEE Definition:

SE is the application of a systematic,

disciplined, quantifiable approach to the

development, operation and maintenance

of software


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Other Definition:

SE deals with cost-effective solutions to

practical problems by applying scientific

knowledge in building software artifacts in

the service of mankind


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Other Definition:

SE is a discipline whose aim is the

production of fault free software that

satisfies the users needs and that is

delivered on time and within budget


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Software Engineering Principles

PRINCIPLES

METHODSANDTECHNIQUES

METHODOLOGIES

TOOLS


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Software Engineering Principles

Rigor and formality

Separation of concernsModularity and decomposition

Abstraction

Anticipation of change

Generality

Incrementality

Scalability

Compositionality

Heterogeneity


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Software Characteristics

1. Most software is custom-built, ratherthan assembled from existing

components.2. Software is developed or engineered;

it is not manufactured in the classicalsense.

3. Software is flexible.

4. Software doesnt wear out.


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The Bathtub Curve

Reliability Studies forHardware Products


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Software Curve

Time

Failure

Intensity

-Software becomesreliable over time

-It becomes

obsolete if the

environment it was

developed changes


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Software Crisis

Crisis problems and causes

encountered in the different stages of

software development


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Software Crisis

ProblemsSchedules and cost estimates are often grossly inaccurate

The Productivity of software people hasnt kept pace with

the demand for their servicesThe quality of the software is sometimes less thanadequate

With no solid indication of productivity, evaluation isimpossible

Communication between developer and customer is oftenpoor

Software maintenance tasks devour the majority of allsoftware funds


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Software Crisis

CausesThe quality of the software is not good becausemost developers use historical data to developthe software

If there is delay in any process or stage thenscheduling does not match the actual timing

Communications can break down because thespecial characteristics of software and problemsassociated with its development aremisunderstood

The software people responsible for tapping thepotential often change when it is discussed andresist change when it is introduced


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Software Crisis from the programmers point of view

Problem of

Compatibility

PortabilityIn documentation

Piracy of software

Coordination of work of differentpeople

Proper maintenance


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Software Crisis from the users point of view

Software cost is very high

Hardware goes down

Problem of different versions ofsoftware

Problem of views

Problem of bugs


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Software Myths

If we get behind schedule, we can add

more programmers and catch up

If we decide to outsource the softwareproduct to a third party, we can just relax

and let that firm build it.

Project requirement continuously changes,

but changes can be easily accommodated

because software is flexible


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Software Myths

The only deliverable work product for a

successful project is the working

program

Software with more features is a better

software

Once we write the program and get itto work, our job is done


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Software Myths

Until we get the program running, we have

no way of assessing its quality

Software engineering will make us createvoluminous and unnecessary

documentation and will invariably slow us

down

A general statement of objectives is

sufficient to begin writing programs; we can

fill in the details later


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Software Applications

Applications are grouped into 8 areas

1. System Software

2. Real-time Software3. Embedded Software

4. Business Software

5. Personal Computer Software

6. Artificial Intelligence Software7. Web-based Software

8. Engineering and Scientific Software


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Software Applications:

System Software

Used to run the system as an

assistance to other software programs

Ex: compilers, editors, utilities, OS

components, drivers, interfaces


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Real-Time Software

Deals with the changing environment;it collects input, converts it to digital,

control component that responds tothe external environment and performsactions

Monitors, controls and analyze real-world events as they occur

Ex: Rocket launching, games, etc.


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Embedded Software

Written to perform certain functions

under control conditions and is further

embedded into hardware as part of alarge systems

Also called intelligent software


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Business Software

Designed to process and drives

business applications through on-line

or real-time mode

Ex: accounting packages, MIS, payroll,

inventory


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Personal Computer Software

Ex: word processing, spreadsheets,

computer graphics, etc.


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AI Software

Uses non-numeric algorithms to solve

complex problems

Ex: robotics, expert systems, pattern

recognition, neural networks, theorem

proving, game playing, signal-

processing software


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Web-Based Software

Included the languages by which web

pages are processed


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Engineering and Scientific Software

Written for specific applications using

the principles and formulae of each

field


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Software Engineering Processes

Process a series of that steps

involving activities, constraints, and

resources that produce an intendedoutput of some kind.

Software Process a set of activities

whose goal is the development orevolution of software


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Four Fundamental process activities:

1. Software Specifications

2. Software Development

3. Software Validation

4. Software Evolution


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Software Specifications

The functionality of the software and

constraints on its operation must be

defined


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Software Development

Software that meets the specifications

must be produced


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Software Validation

The software must be validated to

ensure that it does what the customer

wants


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Software Evolution

The software must evolve to meet

changing customer needs


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Some Terminologies

Deliverables and Milestones

Deliverables are generated during

software development

Milestones are the events that ascertain

the status of the project


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Some Terminologies

Product and Process

Product is what is delivered to the

customer (deliverables)

Process is the way we produce software


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Some Terminologies

Measure, Metrics, Indicators

Measures provides a quantitative

indication of amount, dimension,capacity, or size of a given attribute of aproduct

Metrics are quantitative measure of the

degree to which a system possesses agiven attribute of a product

Indicators are is a combination of metrics


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Programs vs. Software Products

Programs Software Product

Developed by individuals for their

personal use

Developed by a group of engineers

working as a team

Small in size Usually large in size

Single user Large number of users

Single developers Team of developers

Lack proper documentation Good documentation support

Adhoc development Systematic development

Lack of user interface Good user interface

Limited functionality More functionality

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