software & software engineering

7/26/2019 Software & Software Engineering

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Chapter 1

Software & Software Engineering

What is Software?

The product that software professionals build and then support over the long

term.

Software encompasses: (1) instructions (computer programs) that when

executed provide desired features, function, and performance; () data

structures that enables the programs to ade!uatel" store and manipulate

information and (#) documentation that describes the operation and use of

the programs.

Software products

$eneric products

% Stand%alone s"stems that are mar&eted and sold to an" customer

who wishes to bu" them% 'xamples * software such as editing, graphics programs, pro+ect

management tools; *- software; software for specic mar&ets

such as appointments s"stems for dentists.

*ustomi/ed products

% Software that is commissioned b" a specic customer to meet their

own needs.

% 'xamples embedded control s"stems, air tra0c control software,tra0c monitoring s"stems.

Why Software is important?

The economies of developed nations are dependent on software.

2ore and more s"stems are software controlled (transportation,

medical, telecommunications, militar", industrial, entertainment,)

Software engineering is concerned with theories, methods and tools for

professional software development.

'xpenditure on software represents a signicant fraction of $3 in all

developed countries.

Software costs

Software costs often dominate computer s"stem costs. The costs of

software on a * are often greater than the hardware cost.


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Software costs more to maintain than it does to develop. 4or s"stems

with long life, maintenance ma" be several times develop costs.

Software engineering is concerned with cost%e5ective software

development.

Features of Software?

6ts characteristics that ma&e it di5erent from other things human being

build.

4eatures of such logical s"stem

Software is developed or engineered, it is not manufactured in the

classical sense which has !ualit" problem.

Software doesn7t 8wear out9 but it deteriorates (due to change).

ardware has bathtub curve of failure rate (high failure in thebeginning then drop to stead" state, then cumulative e5ects of dust,

vibration, abuse occurs).

lthough the industr" is moving toward component%based construction

(e.g. standard screws and o5%the%shelf integrated circuits,) most

software continues to be (custom build). 2odern reusable components

encapsulate data and processing into software parts to be use b"

di5erent program. '.g. graphical user interface, window, pull%down

menus in librar" etc.

Software Applications

1. S"stem software such as compilers, editors, le management utilities. pplication software: stand%alone programs for specic needs.#. 'ngineeringscientic software: *haracteri/ed b" 8number crunching9

algorithms such as automotive stress anal"sis, molecular biolog",

orbital d"namics etc.


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Software New Categories

Cpen world computing%pervasive, ubi!uitous, distributed computing

due to wireless networ&ing. ow to allow mobile devices, personal

computer, enterprise s"stem to communicate across vast networ&.

3etsourcing the ?eb as a computingengine. ow to architect simpleand sophisticated applications to target end%users worldwide.

Cpen source 8free9 source code open to the computing communit" (a

blessing, but also potential curseD)

Software Engineering e!nition

The Seminal -enition

[Software Engineering is] the establishment and use of

______engineering principles in order to obtain economically software

that is reliable and works eciently on real machines.

The 6''' denition:

Software 'ngineering; (1) The application of a s"stematic disciplined

!uantiable approach to the development operation, and maintenance

of software; that is, the application of engineering to software. () The

stud" of approaches as in (1).

"mportance of Software Engineering

2ore and more, individuals and societ" rel" on advances software

s"stems. ?e need to be able to produce reliable and trustworth"

s"stems economicall" and !uic&l".

6t is usuall" cheaper, in the long run, to use software engineering

methods and techni!ues for software s"stems rather than +ust write

the programs as if it was a personal programming pro+ect. 4or the most

t"pe of s"stem, the ma+orit" of costs are the costs of changing the

software after it has gone into use.

FA# a$out software engineering

#uestion Answer?hat is software *omputer programs, data structures

and associated documentation.

Software products ma" be developed

for a particular customer or ma" be

developed for general mar&et.


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?hat are the good attributes of a

good software

$ood software should deliver the

re!uires functionalit" and

performance to the user and should

be maintainable, dependable and

usable.?hat is software engineeringE Software engineering is an

engineering discipline that is

concerned with all aspects of

software production.?hat is di5erence between software

engineering and computer scienceE

*omputer science focuses on theor"

and fundamentals, software

engineering is concerned with the

practicalities of developing and

delivering useful software.

?hat is the di5erence betweensoftware engineering and s"stem

engineeringE

S"stem engineering is concernedwith all aspects of computer%based

s"stems development including

hardware, software and process

engineering. Software engineering is

the part of this more general process.

Essential attri$utes of good software

%roduct Characteristics escription

2aintainabilit" Software should be written in such a

wa" so that it can evolve to meet the

changing needs of customers. This is

a critical attribute because software

change is an inevitable re!uirement

of a changing business re!uirement.-ependabilit" and securit" Software dependabilit" includes a

range of characteristics including

reliabilit", securit", and safet".

-ependable software should notcause ph"sical or economic damage

in the event of s"stem failure.

2alicious users should not be able to

access or damage the s"stem.'0cienc" Software should not ma&e wasteful

use of s"stem resources such as


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memor" and processor c"cles.

'0cienc" therefore includes

responsiveness, processing time,

memor" utili/ation, etc.cceptabilit" Software must be acceptable to the

users for which it is designed. This

means that it must be

understandable, usable, and

compatible with other s"stems that

the" use.

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