2002 prentice hall chapter 13 systems design & development
TRANSCRIPT
2002 Prentice Hall
Chapter 13
Systems Design & Development
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Topics
How People Make Programs
From Idea to Algorithm
From Algorithm to Program
Programming Languages and Methodologies
System Analysis and the System Life Cycle
The State of Software
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How People Make Programs
Programming is a specialized form of problem solving and involves:
Understanding the Problem– Defining the problem
Designing a Solution– Devising, refining, and testing the algorithm
Implementing the Design– Writing the program
Evaluating the Solution– Testing and debugging the program
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From Idea to Algorithm
A school teacher needs a program to play a number-guessing game so students can learn to develop logical strategies and practice their arithmetic. In this game the computer picks a number between 1 and 100 and gives the player seven turns to guess the number. After each incorrect try the computer tells the player whether the guess is too high or too low.
Start with a statement of the problem:
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From Idea to Algorithm: Stepwise Refinement
The first cut at the problem breaks it into three parts: a beginning, a middle, and an end. Each of these parts represents a smaller programming problem to solve.
BeginGame
Repeat Returnuntil Number is
Guessed
EndGame
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From Idea to Algorithm: Step Refinement
The next refinement fills in a few details for each part.
1. Begin Game
Display instructionsPick a number between 1 and 100
2. Repeat Turn Until Number is Guessed
Input guess from user Respond to guess End Repeat
3. End Game
Display end message
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From Idea to Algorithm: Stepwise Refinement
Fill in the crucial details. How to respond to guess
If guess = number, then say so and quit;if guess < number, then say guess is too small;if guess> number, then say guess is too high.
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From Idea to Algorithm: Step Refinement
Give the computer a way of knowing when seven turns have passed.
begin game display instructions pick a number between
1 and 100 set counter to 0
repeat turn until number is guessed or counter = 7 input guess from user if guess = number, then say so and quit; else if guess < number, then say guess is too small; else say guess is too big add 1 to counter
end repeatend game
display end message
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From Idea to Algorithm: Control Structures
Logical structures that control the order in which instructions are carried out
Three basic control structures: Sequence--group of instructions followed in order
from first to last Selection--to choose between alternative courses of
action depending on certain conditions. Repetition--allows a group of steps to be repeated
several times, usually until some condition is satisfied
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From Idea to Algorithm: Testing
This round of testing is designed to check the logic of the algorithm
Test the algorithm by following the instructions using different sets of numbers.
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From Algorithm to Program
A simple program contains:
The program heading The declarations and definition The body
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Into the Computer
A text editor is used to enter and save the program.
Use either a translator or compiler to translate the program into machine language.
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Translation Software
Translation software, called an interpreter, translates a high-level program to a machine language one statement at a time during execution.
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Compiler
A compiler translates an entire high-level program to machine language before executing the program.
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Programming Languages & Methodologies
Machine language is the native language of a computer.
Instructions for the four basic arithmetic operations, for comparing pairs of numbers, for repeating instructions, and so on all binary
Instructions, memory locations, numbers, and characters are all represented by strings of zeros and ones
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Programming Languages & Methodologies
An assembler translates each statement of assembly language into the corresponding machine-language statement.
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High Level Languages
High level languages fall somewhere between natural human languages and precise machine languages
Examples: C++, Java, Basic, FORTRAN, COBOL
They are easier to write, debug and are transportable between machines.
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Structured Programming
Structured programming is a technique to make the programming process easier and more productive.
A program is well structured if:- It’s made up of logically cohesive modules- The modules are arranged in a hierarchy- It’s straightforward and readable.
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Unstructured Programming
An unstructured program is like a huge, complicated machine that can’t be easily broken down into sections.
Any modification would require the entire machine to be disassembled.
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Structured Programming
problems can be isolated to individual modules
the input and output of each module in the assembly line are easier to understand
Structured programs are easier to understand and modify because:
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Object-Oriented Programming
In object-oriented programming a program is not just a collection of step-by-step instructions or procedures; it’s a collection of objects.
Objects contain both data and instructions.
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Object Oriented Programming
With OOP technology, programmers can build programs from prefabricated objects in the same way builders construct houses from prefabricated walls.
For example, an object that sorts addresses in alphabetical order in a mailing list database can also be used in a program that sorts hotel reservations alphabetically.
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Visual Programming
Visual programming tools allow programmers to create large portions of their programs by drawing pictures and pointing to on-screen objects, eliminating much of the tedious coding of traditional programming.
Apple’s HyperCard was probably the first popular example of a visual programming environment.
Today Microsoft’s Visual Basic is widely used by professionals and hobbyists alike because of its visual approach to programming.
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Languages for Users
User-oriented macro languages or scripting languages that allow users to create programs, called macros, that automate repetitive tasks
Fourth-generation languages (4GL) - English-like phrases and sentences to issue instructions Nonprocedural; focus on what needs to be done, not on how to do it
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Programming for the Web
HTML JavaScript Java Perl XML
Programmers can, and do, use a variety of languages, including C and C++, to write Web applications. But some programming tools are particularly useful for developing Web applications:
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The Future of Programming
Programming languages will continue to evolve in the direction of natural languages like English.
The line between programmer and user is likely to grow hazy.
Computers will play an ever-increasing role in programming themselves
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System Analysis and the System Life Cycle
Information systems—collections of people, machines, data, and methods organized to accomplish specific functions and to solve specific problems
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The Systems Development Life Cycle
The graphical “waterfall”model of the SDLC showsa basic sequential flow fromidentifying the “right things to do” to making sure that“things are done right.”
Investigation
Analysis
Design
Development
Implementation
Maintenance
Retirement
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The Systems Development Life Cycle
Investigation
Define the problem:
•identify the information needs of the organization •examine the current system•determine how well it meets the needs of the organization •study the feasibility of changing or replacing the current system
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The Systems Development Life Cycle
Analysis
During the analysis phase the systems analyst :
• gathers documents• interviews users of the current system• observes the system in action • generally gathers and analyzes data to understand
the current system and identify new requirements
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The Systems Development Life Cycle
Prototyping is an interactive methodology in which the prototype is continually modified and improved until it meets the needs of the end-user.
Identifyrequirements
Develop workingmodel of system
Use Prototype
Evaluate featuresof prototype
Develop application, install prototype forevaluation by end users,begin new prototype, orabandon application.
Additionalchanges toprototypeneeded.
Design
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The Systems Development Life Cycle
The systems analyst must plan and schedule carefully activities in the development phase of the SDLC because they can overlap and occur simultaneously.
Testing
Documenting
Scheduling
Programming
Purchasing
Development
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The Systems Development Life Cycle
Implementation
•Direct cutover approach•Parallel systems approach•Phase-in approach•Pilot approach
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The Systems Development Life Cycle
Maintenance
The maintenance phase involves monitoring, evaluating, repairing, and enhancing the system throughout the lifetime of the system.
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The Systems Development Life Cycle
Retirement
Systems are often used for many years, but at some point in the life of a system, ongoing maintenance is not enough..
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The Science of Computing
Many computer scientists prefer to call the field computing science because it focuses on the process of computing rather than on computer hardware.
Computer science includes a number of focus areas: Computer theory Algorithms Data structures Programming concepts and languages Computer architecture Management information systems Software engineering
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The State of Software: Software Problems
Software errors are difficult to locate and more difficult to remove.
Errors of omission Syntax errors Logic errors Clerical errors Capacity errors Judgment errors
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The State of Software: Software Solutions
Programming techniques
Programming environments
Program verification
Clean-room programming
Human management
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