Chapter Twelve - Columbus State University

Chapter TwelveChapter Twelve

Systems Design and Development

©1999 Addison Wesley Longman 12.2

After reading this chapter, you should be able to:

• Describe the process of designing,programming, and debugging a computerprogram

• Explain why there are many differentprogramming languages and give examplesof several

• Explain why computer languages are builtinto applications, operating systems andutilities


After reading this chapter, you should be able to:

• Outline the steps in the life cycle of aninformation system and explain the purposeof program maintenance

• Explain the relationship between computerprogramming and computer science

• Describe the problems faced by softwareengineers in trying to produce reliable largesystems


Chapter Outline

• How People Make Programs• The Languages of Computers

• Programs in Perspective: SystemsAnalysis and the System Life Cycle

• The Science of Computing• The State of Software


How People Make Programs

• Problem solving process involves:– Understanding the problem– Devising a plan for solving the problem– Carry out the plan– Evaluating the solution


How People Make Programs

Programs aresolutions toproblems.

Programming is aspecialized form ofproblem solving.


Four-Step Processto Programming

Define the problem:make sure you knowwhat the problem is.

Devise, refine, andtest the algorithm:break the probleminto smaller,solvable parts(stepwiserefinement).


Four-Step Processto Programming

Write the program: begin withpseudocode and eventually use acomputer language.

Test and debug the program: to makesure it solves the initial problem thatwas defined.


From Idea to Algorithm

Stepwise Refinement: complexproblems will need to be broken intosmaller problems.

Control Structures: logical structuresthat control the order in which theinstructions the computer is to follow.

Testing the Algorithm: check the logic.


Stepwise Refinement

A complex problem likewriting a computergame needs to bebroken into threeparts: a beginning, amiddle, and an end.

Further refinementadds more detail toeach part.

For example:• begin the game• repeat player’s turn until

the player guesses rightanswer or seven turns arecompleted

• end the game


Control Structures

Sequence:instructions arefollowed in theorder given.

Selection:instructions arebased on logicaldecisions.

Display instructionspick a number between 1 and 100set counter to 0

if guess < number, thensay guess is too small;else say guess is too big


Control Structures

Repetition:instructions arerepeated untilsome condition issatisfied.

repeat turn until number isguessed or counter = 7

input guess from useradd 1 to counterend repeat


From Algorithm to Program

If the logic of thealgorithm testsaccurately, it canthen be written intoa program.

Writing a program iscalled coding.


From Algorithm to Program

The program will have three parts:Program heading contains the name of the

program and data files.Declarations and definitions of variables

and other programmer-defined items.Body contains the instructions the computer

will follow.


Into the Computer

Next, the program needs to be enteredinto the computer using a text editor.

Once typed into a text editor, it can besaved to disk.

To run or execute the program, it must betranslated into machine language bymeans of an interpreter or compiler.


Interpreters and Compilers

• Interpreter: eachinstruction istranslatedindividually

• Compiler: theentire program istranslated intomachine language.


The Languages of Computers

Every computer has anative language - amachine language.

Machine language andAssembly language:– Difficult to learn and

use.– Examples include

machine andassembly languages.


The Languages of Computers

High-level Languages:– English-like vocabulary.– Transportable– Examples include C++, LOGO, and BASIC.


Multilingual Machines

Well known high-level programminglanguages include:FORTRAN (Formula Translation): the first

commercial high-level language.COBOL (Common Business Oriented Language):

developed for business data processingproblems.



Well known high-level programminglanguages include:LISP (List Processing): developed to process

non-numeric data like characters, words,and other symbols.

BASIC (Beginners All-purpose SymbolicInstruction Code): developed as an easy-to-learn language for beginners.



Pascal: designed toencouragestructuredprogramming.

C: developed as atool forprogrammingoperating systemssuch as UNIX.



Ada: is a massive languagedeveloped for the USGovernment

PROLOG: designed forworking with logicalrelationships betweenfacts

LOGO: is a dialect of LISPspecially designed forchildren.


Programming Methodologies

StructuredProgramming: atechnique to makethe programmingprocess easier andmore productive bywriting many smallprograms.



• A program is wellstructured if it is:– made up of logically

cohesive modules– arranged in a

hierarchy– straightforward and

readable



Object-orientedProgramming: theprogram is acollection ofinteractive objectsthat contain bothdata andinstructions.



• VisualProgramming:programmerswrite programs bydrawing picturesand pointing toobjects on thescreen.


Languages for Users

Languages designedto meet the needs ofmost computerusers include:

Macro or scriptinglanguages: used inautomating arepetitive task.


Languages for Users

Fourth-generation languages (4GLs):easier to use and more like naturallanguage. Characteristics include:- English-like phrases- Non-procedural- Increases productivity

Querying a database with a querylanguage is one example.


Languages for Users

• Component Software: users constructsmall custom applications from softwarecomponents.– Plug-ins for Netscape Navigator and

Internet Explorer– JavaScript


The Future of Programming

Trends:– Natural languages and artificial intelligence

will provide users with programming toolsthat will understand the language of theuser.

– The distinction between user andprogrammer will begin to fade. Users won’tneed to master complicated programminglanguages to construct applications.


The Future of Programming

– Programs will program themselves basedon simple descriptions provided by theuser.


Systems Analysis and theSystems Life Cycle

Programs are only part of largerinformation systems - collections ofpeople, machines, data, and methodsorganized to accomplish specificfunctions and to solve a problem.


Systems Analysis and theSystems Life Cycle

System Life Cycle - a sequence of stepsor phases it passes through betweenthe time the system is conceived andthe time it is phased out.

Systems analyst - a computerprofessional primarily responsible fordeveloping and managing a system as itprogresses through these phases.


The Systems DevelopmentLife Cycle

The systems developmentlife cycle is a sequenceof steps followed by aproject team.

Investigation: “Why isthere a problem?”

Analysis: “What is theproblem?”

Design: “How can theproblem be solved?”


The Systems DevelopmentLife Cycle

Development: teams of programmers andothers begin developing the various parts ofthe system.

Implementation: the system is put to work.Maintenance: ongoing upgrades.Retirement: phasing out the current system.


Investigation

Systems investigation involves definingthe problem - identifying the informationneeds of the organization, examiningthe current system, needs oforganization, and studying feasibility ofchanging systems.

This phase produces a feasibility study.


Analysis

The systems analystgathers documents,interviews users,observes the system inaction, and generallygathers and analysesdata to understand thecurrent system.


Design

In the design phase,the systems analystdevelops the systemspecifications thatdescribe howexactly the systemrequirements will bemet.


Design

The systems analystconsiders:– user interface

design.– database design.– process design.


Development

The development phase is a process ofturning the design specifications into areal working system.

The initial testing of the system is knownas alpha testing and potential usersdo beta testing after the bugs areworked out.


Development

Development includesa complex mix ofscheduling;hardware, software,and communicationspurchasing;documentation; andprogramming.


Implementation

This phase may involve extensive trainingand technical user support.

Implementation includes user educationand training, equipment replacement,file conversion, and careful monitoringof the new system for problems.


Maintenance

The maintenancephase involvesmonitoring,evaluating,repairing, andenhancing thesystem throughoutthe life cycle.


Retirement

At some point in the life of asystem, on-goingmaintenance is not enough.The needs of anorganization change, users’expectations change, andthere is always newtechnology available.


The Science of Computing

• Computer theory - applies concepts oftheoretical mathematics tocomputational problems.

• Algorithms - logical underpinnings ofcomputer programs.

• Data structures - define the logicalstructure of data



• Programming concepts andlanguages - have evolved throughgenerations.

• Computer architecture - deals with theway hardware and software worktogether.



• Management information systems(MIS) - is part computer science, partbusiness.– MIS specialist focus on developing

systems in timely, reliable and usefulinformation to manager in business.

– MIS applies theoretical concepts ofcomputer science to real-world problems.



• Software engineering - is a relativelynew branch of computer science thatattempts to apply engineering principlesand techniques to the less-than-concrete world of computer software.


The State of Software

The problems faced bysoftware engineersaffect all of us.

Two inherent problemsin softwaredevelopment arecost and reliability.


Software Problems

Cost:The cost of hardware has dropped but the

cost of developing software has continuedto rise.

Reliability:Software errors include errors of omission,

syntax, logic, clerical, capacity, andjudgement.


Software Solutions

Responding to the cost and reliabilityissues, computer scientists are workingto improve:– Programming Techniques– Programming Environments– Program Verification– Clean Room Programming– Human Management

Chapter Twelve - Columbus State University

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