software engineering lecture 1

8/6/2019 Software Engineering Lecture 1

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Software - is a collection ofcomputer programs and related

data that provide theinstructions for telling acomputer what to do and howto do it.


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In other words, software is aconceptual entity which is a

set of computer programs,procedures, and associateddocumentation concerned with

the operation of a dataprocessing system


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We can also say softwarerefers to one or more computer

programs and data held in thestorage of the computer forsome purposes. Software is a

set of programs, procedures,algorithms and itsdocumentation


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Program software performs thefunction of the program it

implements, either by directlyproviding instructions to thecomputer hardware or by

serving as input to anotherpiece of software.


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Software is the easiest wayfor users to interact with the

hardware of a system.W

ithmodern day computers, it wouldbe impossible to accomplish

anything without software. Thebest you could accomplishwithout software would be


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clocks (analog and basic digital)and things like that.

Software is what allowscomplicated computations.Everything you use has a

software.Windows/MAC/Linux/UNIX areall software's.


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What more? every electronicdevice you use has a software.I

n short, software provide theelectrical instructions to thehardware. Without software,

the computer revolution isundone.


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Software evolution - is theterm used in software

engineering (specificallysoftware maintenance) to referto the process of developing

software initially, thenrepeatedly updating it forvarious reasons.


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The aim of software evolutionwould be implementing (and

revalidate) the possible majorchanges to the system withoutbeing able a priority to predict

how user requirements willevolve


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1. The existing larger systemis never complete and continues

to evolve2. As it evolves, thecomplexity of the system will

grow unless there is a bettersolution available to solve theseissues.


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The main objectives ofsoftware evolution are ensuring

the reliability and flexibility ofthe system. During the 20years pasted, the lifespan of a

system could be in average 6-10 years.


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However, recently found that asystem should be evolved once

few months to ensure it iscompromised to the real-worldenvironment.


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This is due to the rapid growthof World Wide Web and

Internet Resources that makeusers easier to find relatedinformation. The idea of

software evolution leads to opensource development as anybody


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could download the sourcecodes and hence modify it. The

positive impact in this case islarge amounts of new ideaswould be discovered and

generated that aims thesystem to have betterimprovement in variety choices.


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However, the negative impactis there is no copyright if asoftware product has beenpublished as open source.


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Software Components -A computer system consists of

three major components:hardware, software, andhumans (users, programmers,

administrators, operators,etc.).


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Software can be furtherdivided into seven layers.

Firmware can be categorized aspart of hardware, part ofsoftware, or both.

The seven layers of softwareare (top to bottom


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Programs; System Utilities;Command Shell; System

Services; User Interface;Logical Level; and HardwareLevel. A Graphics Engine

straddles the bottom threelayers


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only the bottom two levels arethe operating system, although

even technical persons willoften refer to any level otherthan programs as part of the

operating system


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The following are examples ofeach category:Programs: Examples of Programs

include your word processor,spreadsheet, graphics programs,music software, games, etc.

System Utilities: Examples ofSystem Utilities include file copy,hard drive repair, and similar


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items. On the Macintosh, allthe Desk Accessories

(calculator, key caps, etc.) andall of the Control Panels areexamples of System Utilities.


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Command Shell: The CommandShell on the Macintosh is theFinder and was the first

commercially available graphiccommand shell. On Windows, theCommand Shell is a poorlyintegrated combination of theFile Manager and the Program

Manager.


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The command line (C:\ prompt)of MS-DOS or Bourne Shell ofUNIX are examples of the olderstyle text-based commandshells.

System Services: Examples ofSystem Services are built-indata base query


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languages on mainframes or theQuickTime media layer of the

Macintosh.User Interface: Until theMacintosh introduced Alan

Kays (inventor of the personalcomputer, graphic userinterfaces, object oriented


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programming, and softwareagents) ground breaking ideas

on human-computer interfaces,operating systems didnt includesupport for user interfaces

(other than simple text-basedshells). The Macintosh userinterface is called the


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Macintosh Tool Box andprovides the windows, menus,

alert boxes, dialog boxes,scroll bars, buttons, controls,and other user interface

elements shared by almost allprograms.


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Logical Level of OperatingSystem: The Logical Level of

the operating system provideshigh level functions, such asfile management, internet and

networking facilities, etc.


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Hardware Level of OperatingSystem: The Hardware Level

of the operating systemcontrols the use of physicalsystem resources, such as the

memory manager, processmanager, disk drivers, etc.


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Graphics Engine: The GraphicsEngine includes elements at all

three of the lowest levels,from physically displayingthings on the monitor to

providing high level graphicsroutines such as fonts andanimated sprites.


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Human users normally interact withthe operating system indirectly,through various programs

(application and system) andcommand shells (text, graphic,etc.), The operating system

provides programs with servicesthrough system programs andApplication Program Interfaces

(API

s).


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Characteristic of Software -One of the challenges of

software quality is that"everyone feels they understandit. In addition to more software

specific definitions given below,there are several applicabledefinitions of quality which are


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are used in business. Softwarequality may be defined asconformance to explicitly

stated functional andperformance requirements,explicitly documenteddevelopment standards andimplicit characteristics that


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that are expected of allprofessionally developed

software. The three keypoints in this definition:1.Software requirements are

the foundations from whichquality is measured.


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2. Specified standards define aset of development criteria

that guide the management insoftware engineering.If criteria are not followed

lack of quality will usuallyresult.


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3. A set of implicitrequirements often goes

unmentioned, for example easeof use, maintainability etc.If software conforms to its

explicit requirements but failsto meet implicit requirements,software quality is suspected.


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Another definitionCharacteristics of Software

it divides software into twopieces: internal and externalquality. External quality

characteristics are those partsof a product that face itsusers,


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where internal qualitycharacteristics are those that

do not.Another definition "a productquality is a function of how

much it changes the world forthe better. This can beinterpreted as meaning that


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user satisfaction is moreimportant than anything in

determining software quality.Another definition, softwarecharacteristics is value to some

person." This definitionstresses that quality isinherently subjective


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subjective - different people willexperience the quality of the samesoftware very differently. One

strength of this definition is thequestions it invites software teamsto consider, such as "Who are the

people we want to value oursoftware?" and "What will bevaluable to them?"


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Software applicationsApplication software, also

known as an application or an"app", is computer softwaredesigned to help the user to

perform singular or multiplerelated specific tasks.Examples include enterprise


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enterprise software, accountingsoftware, office suites,

graphics software and mediaplayers. Many applicationprograms deal principally with

documents. Apps may bebundled with the computer andits system software, or may


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be published separately. Someusers are satisfied with the

bundled apps and need neverinstall one.Application software is

contrasted with systemsoftware and middleware,which manage and integrate


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a computer's capabilities, buttypically do not directly apply

them in the performance oftasks that benefit the user.The system software serves

the application, which in turnserves the user.


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Similar relationships apply inother fields. For example, ashopping mall does not provide

the merchandise a shopper isseeking, but provides space andservices for retailers that serve

the shopper. Rail tracks similarlysupport trains, allowing thetrains to transport passengers.


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Application software applies thepower of a particular computingplatform or system software to a

particular purpose. Some apps suchas Microsoft Office are availablein versions for several different

platforms; others have narrowerrequirements and are thus called,for example, a


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Geography application forWindows or an Android applicationfor education or Linux gaming.

Sometimes a new and popularapplication arises which only runson one platform, increasing thedesirability of that platform. Thisis called a killer application.

software engineering lecture 1

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