Beekman5 std ppt_13

2002 Prentice Hall

Chapter 13

Systems Design & Development

2002 Prentice Hall 2

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


How People Make Programs

Programming is a specialized form of problem solving and involves:

Defining the problem Devising, refining, and testing the algorithm Writing the program Testing and debugging the program


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:


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


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


From Idea to Algorithm: Stepwise Refinement

Fill in the crucial details.

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.


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


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


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.


From Algorithm to Program

A simple program contains:

The program heading The declarations and definition The body


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.


Translation Software

Translation software, called an interpreter, translates a high-level program to a machine language one statement at a time during execution.


Compiler

A compiler translates an entire high-level program to machine language before executing the program.


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


Programming Languages & Methodologies

An assembler translates each statement of assembly language into the corresponding machine-language statement.


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.


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.


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.


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:


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 and can send and receive messages.


The Three Faces of Basic

1. Early BASIC - The program with numbered lines. Statements are executed in numerical order unless control is transferred to another statement with a GoTo statement.

2. Structured BASIC - The modular program with many structured programming features. The main program has been reduced to a handful of statements at the top of the listing. These statements display the overall logic of the program. As it is running, the main program uses Call statements to transfer control to each subprogram.

3. Visual BASIC- A modern programming environment that includes many of the ideas and tools of object-oriented programming.


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.


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.


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


Component Software

Construct small custom applications from software components

Customizability is possible only if applications are programmed to allow it. More and more software programs, including operating systems, are designed with extensibility in mind.


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:


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



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



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



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



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



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



Implementation

•Direct cutover approach•Parallel systems approach•Phase-in approach•Pilot approach



Maintenance

The maintenance phase involves monitoring, evaluating, repairing, and enhancing the system throughout the lifetime of the system.



Retirement

Systems are often used for many years, but at some point in the life of a system, ongoing maintenance is not enough..


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


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


The State of Software: Software Solutions

Programming techniques

Programming environments

Program verification

Clean-room programming

Human management


Beekman5 std ppt_13

Technology

guess number

program programming

program testing

simple program

input guess

programs programming

entire highlevel program

game display instructions