Chapter+1+Introduction+part+1

7/26/2019 Chapter+1+Introduction+part+1

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Chapter : Introduction toSoftware Engineering

Ref. book :

Software Engineering by Roger Pressman


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Chapter : Topic Covered

Evoving Roe of Software

!ardware vs. Software

Software characteristics

Changing nature of software Evoution of Software

Software "yths

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Evoving Roe of Software

Software is a product Transforms information $ produces% manages% ac&uires%

modifies% dispays% or transmits information

'eivers computing potentia of hardware and networksSoftware is a vehice for deivering a product Contros other programs (operating system)

Effects communications (networking software)

!eps buid other software (software toos *environments)

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,hat is Software -

Software can be defined as: Instruction e/ecuted provide desire features% function *

performance. 'ata structure to ade&uatey manipuate operation. 'ocuments operation and use of the program.

Software products may be deveoped for a particuar customer or may bedeveoped for a genera market.

Software products may be Generic$ deveoped to be sod to a range of different

customers e.g. PC software such as E/ce or ,ord.

Bespoke(custom) $ deveoped for a singe customeraccording to their specification.

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!ardware vs. Software

!ardware Software

"anufactured

wear out

1uit using components

Reativey simpe

'eveoped2 engineered

deteriorate

Custom buit

Compe/

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"anufacturing vs. 'eveopment

4nce a hardware product has beenmanufactured% it is difficut or impossibe tomodify. In contrast% software products are

routiney modified and upgraded. In hardware% hiring more peope aows you

to accompish more work% but the samedoes not necessariy hod true in softwareengineering.

5nike hardware% software costs areconcentrated in design rather thanproduction.

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7aiure curve for !ardware

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7aiure curve for Software

,hen a hardware component wears out% it is repaced by a spare part.

There are no software spare parts. Every software faiure indicates anerror in design or in the process through which design was transatedinto machine e/ecutabe code. Therefore% software maintenance invoves

consideraby more compe/ity 9


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Component 1ased vs. Custom 1uit

!ardware products typicay empoymany standardied designcomponents.

"ost software continues to be custombuit.

The software industry does seem tobe moving (sowy) towardcomponent$based construction.

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Software characteristics

Software is deveoped or engineered< it is notmanufactured.

Software does not =wear out> but it doesdeteriorate.

Software continues to be custom buit% asindustry is moving toward component based

construction.

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System Software: System software is a coection of programs written to service other programs.

It is characteried by heavy interaction with computer hardware< heavy usage bymutipe users< concurrent operation that re&uires scheduing% resource sharing%and sophisticated process management< compe/ data structures< and mutipee/terna interfaces.

Ex. Compiers% operating system% drivers etc.

Appication Software : Appication software consists of standaone programs that sove a specific

business need.

Appication software is used to contro the business function in rea$time.

Engineering 2Scientific software: Characteried by Bnumber crunchingB agorithms. Appications range from astronomy to vocano ogy% from automotive stress

anaysis to space shutte orbita dynamics% and from moecuar bioogy toautomated manufacturing.

Ex. Computer Aided 'esign (CA')% system stimuation etc. ?#


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Embedded Software:

It resides in read$ony memory and is used to contro products andsystems

Embedded software can perform imited and esoteric functions.

Ex. keypad contro for a microwave oven.

Product line software:

'esigned to provide a specific capabiity for use by many differentcustomers% product ine software can focus on a imited and esotericmarketpace.

Ex.,ord processing% spreadsheet% C% mutimedia% etc.Web Applications:

,eb apps can be itte more than a set of inked hyperte/t fies.

It evoving into sophisticated computing environments that not onyprovide standaone features% functions but aso integrated withcorporate database and business appications.

Artificial Intelligence software AI software makes use of non$numerica agorithms to sove compe/

probems that are not amenabe to computation or straightforwardanaysis

Ex. Robotics% e/pert system% game paying% etc.

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SoftwareDew Categories4pen word computingDpervasive%ubi&uitous% distributed computing

due to wireess networking. !ow to aow mobie devices% personacomputer% enterprise system to communicate across astnetwork.

etsourcingDthe ,eb as a computing engine. !ow to architectsimpe and sophisticated appications to target end$users wordwide.

4pen sourceD>free> source code open to the computing community(a bessing% but aso a potentia curseF)

Aso G 'ata mining

rid computing Cognitive machines

Software for nanotechnoogies

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Hegacy Software

'efinition

uaity in Hegacy Systems

,hy do egacy systems evove overtime-

otion of Evoution

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Software Evoution

The Haw of Continuing Change (?;80): E$type (Reaword impemented) systems must be continuayadapted ese they become progressivey ess satisfactory.

The Haw of Increasing Compe/ity (?;80): As an E$typesystem evoves its compe/ity increases uness work isdone to maintain or reduce it.

The Haw of Sef Reguation (?;80): The E$type systemevoution process is sef$reguating with distribution ofproduct and process measures cose to norma.

The Haw of Conservation of 4rganiationa Stabiity(?;9@): The average effective goba activity rate in anevoving E$type system is invariant over product ifetime.

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What is SoftwareWhat is Software

Engineering?Engineering?Software Engineering = Software + Engineering

What is Software?

Software = Soft + ware

Any examples?

What is Engineering?

Engineering = Engine-er-ing

Any examples?

Is this an Engineering discipline? If yes, why? If not, why not?

Is this for an Engineer or a scientist?

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What is SoftwareWhat is Software

Engineering?Engineering?A historical defnition:

The establishment and use of sound engineeringprinciples in order to obtain economically software

that is reliable and works eciently on realmachines [Fritz auer, at the !st"#T$ %onference on&oftware Engineering, !'(')

IEEE defnition:

&oftware engineering is the application of asystematic, disciplined, *uanti+able approach tothe deelopment, operation, and maintenance ofsoftware- that is, the application of engineering tosoftware.

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0/anagement0/anagement

1erspecties21erspecties2



#s long as there are good standards andclear procedures in my company, I shouldn3tbe too concerned.

But the proo o the puddingis in the eating;

not in the Recipe !

#@


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#s long as my software engineers042 haeaccess to the fastest and the mostsophisticated computer enironments and

state5of5the5art software tools, I shouldn3t betoo concerned.

The environment isonly one o the several actors

that determine the qualityo the end sotare product!

#?


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6hen my schedule slips, what I hae to do is to

start a +re5+ghting operation7 add moresoftware specialists, those with higher skills and

longer e8perience 5 they will bring the schedule

back on the rails4

nortunately"

sotare #usiness does notentertain schedule compaction

#eyond a limit!

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& ft / th& ft / th

&oft are / ths&oftware /yths


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&oftware /yths&oftware /yths

0


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& ft / th& ft / th



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0


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oehm3soehm3sTop TenTop Ten

IndustrialIndustrial

&oftware&oftware/etrics/etrics

oehm3soehm3s

Top TenTop Ten

IndustrialIndustrial

&oftware&oftware/etrics/etrics#9


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Industrial &oftwareIndustrial &oftware

/etrics/etrics


/etrics/etrics

Finding and +8ing a

software problem afterdeliery of the product is!>> times more e8pensiethan defect remoal during

re*uirements and earlydesign phases.

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#;


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Eort to @epair &oftwareEort to @epair &oftware

0when defects are detected at0when defects are detected at

dierent stages2dierent stages2

Eort to @epair &oftwareEort to @epair &oftware

0when defects are detected at0when defects are detected at

dierent stages2dierent stages2

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% l ti E t f%umulatie Eects of

%umulatie Eects of%umulatie Eects of


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ErrorError


ErrorError

the real problemthe real problemthe real problemthe real problem

correctcorrectcorrectcorrect incorrectincorrectincorrectincorrect hiddenhiddenhiddenhidden missingmissingmissingmissing

requirementsrequirements

+#

% l ti E t f% l ti E t f

%umulati e Eects of%umulatie Eects of


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incorrectincorrectincorrectincorrect


ErrorError


ErrorError


requirementsrequirements

correctcorrectcorrectcorrect incorrectincorrectincorrectincorrect

hiddenhiddenhiddenhidden missingmissingmissingmissing

designdesign


++




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ErrorError


ErrorError


designdesign

correctcorrectcorrectcorrect incorrectincorrectincorrectincorrect

hiddenhiddenhiddenhidden missingmissingmissingmissing

codecode


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/etrics/etrics


/etrics/etrics

/aintenance costs twicewhat the deelopmentcosts.33

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/etrics/etrics


/etrics/etrics


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/etrics/etrics


/etrics/etrics

Dariations in humansaccount for the greatestariations in productiity.55

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#s long as my software engineers042

hae access to the fastest and the mostsophisticated computer enironmentsand state5of5the5art software tools, Ishouldn3t be too concerned.

0@


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/etrics/etrics


/etrics/etrics

The ratio of software to

hardware costs has gonefrom !B7B in !'B andcontinues to grow in

faour of software as thedominant cost.

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0?


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/etrics/etrics


/etrics/etrics

#pplications products

cost three times as muchper instruction asindiidual programs-system software productscost nine times as much.

!!

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/etrics/etrics


/etrics/etrics

6alkthroughs catch (>Cof the errors.""

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&oftware /yths&oftware /yths0


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/etrics/etrics


/etrics/etrics

/any software processesobey a 1areto distribution.

2#$2#$

modulesmodules!#$!#$

costcost

1#1#

0;


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/etrics/etrics


/etrics/etrics


1#1#2#$2#$


errorserrors

3@


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/etrics/etrics


/etrics/etrics


2#$2#$

modulesmodules

!#$!#$

costcostto %i&to %i&

1#1#

3?

' h ( T T

' h ( T T'oehm(s Top Ten


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'oehm(s Top Ten'oehm(s Top Ten)ndustrial *o%t+are ,etrics)ndustrial *o%t+are ,etrics

'oehm(s Top Ten'oehm(s Top Ten)ndustrial *o%t+are ,etrics)ndustrial *o%t+are ,etrics

2#$2#$


e&ec timee&ec time


1#1#

3#


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/etrics/etrics


/etrics/etrics


2#$2#$

toolstools!#$!#$

useuse

1#1#

3+

& ft %h t i ti& ft %h t i ti


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&oftware %haracteristics&oftware %haracteristics&oftware %haracteristics&oftware %haracteristics

is deeloped or engineered,rarely manufactured

is custom5built- rarely assembled

is non5material,and therefore does not wear out

is too ;e8ible

is too pliable0easy to bent:shape2

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&ymptom of &oftware %risis&ymptom of &oftware %risis


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&ymptom of &oftware %risis&ymptom of &oftware %risis

about =&GAB> billion spent peryear in the =& on applicationdeelopment

of this, about =&G!H> billionwasted due to the pro9ectsgetting abandoned or reworked-this in turn because of notfollowing best practices andstandards

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-e%. *tandish /roup0 1""6-e%. *tandish /roup0 1""6

f f


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&ymptom of &oftware&ymptom of &oftware

%risis%risis

!>C of client:serer apps areabandoned or restarted from scratch

A>C of apps are signi+cantly altered toaoid disaster

H>C of apps are deliered signi+cantlylate

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*ource. 3 year study o% 7# large cs apps in 3*ource. 3 year study o% 7# large cs apps in 3

Compu+are 12"5Compu+are 12"5

Wh S ftWh S ft


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Why SoftwareWhy Software

Engineering?Engineering?

sed + e&tensie re+or80

but later abandoned

2#$

Used as delivered

2%Usable w. rework

3%

9 software projects totaling $96.7 million:Where The Money Went

[Report to Congress Comptroller !eneral"979# Deliered0 but neer

success%ully used45$

9aid %or0 but

not deliered3#$ Why?

Software hurts

Requirement

Documents

Chapter+1+Introduction+part+1