Computer Confluence 7/e

Computer Confluence 7/e
© 2006 Prentice-Hall, Inc.

Computer Confluence 7/e
Chapter 14 Systems Design and Development © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Objectives
Describe the process of designing, programming, and debugging a computer program Explain why there are many different programming languages and give examples of several of these languages Explain why computer languages are built into applications, operating systems, and utilities Outline the steps in the life cycle of an information system and explain the purpose of program maintenance © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Objectives (continued)
Explain the relationship between computer programming and computer science Describe the problems faced by software engineers in trying to produce reliable large systems Explain why software companies provide only limited warranties for their products © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Grace Murray Hopper Sails on Software
Grace Murray Hopper helped chart the course of the computer industry from its earliest days Hopper earned a Ph.D. from Yale University in 1928 and taught math for ten years at Vassar College before joining the U.S. Naval Reserve in 1943 The Navy assigned her to the Bureau of Ordnance Computation at Harvard University, where she worked with Howard Aiken’s Mark I, the first large-scale digital computer Hopper wrote programs and operating manuals for the Mark I, Mark II, and Mark III © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Grace Murray Hopper Sails on Software
After World War II, Hopper left Harvard to work on the UNIVAC I, the first general purpose commercial computer, as well as other commercial computers She played central roles in the development of the first compiler (a type of computer language translator that makes most of today’s software possible) and COBOL, the first computer language designed for developing business software Hopper’s greatest impact was probably the result of her tireless crusade against the “We’ve always done it that way” mind-set In the early days of computing, she worked to persuade businesses to embrace new technology In later years, she campaigned to shift the Pentagon and industry away from mainframes and toward networks of smaller computers © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 How People Make Programs
Programming is a specialized form of problem solving Typically involves four steps: Understand the problem. The most important step in the problem-solving process Devise a plan for solving the problem. What resources are available and how might they be put to work to solve the problem? Carry out the plan. Often overlaps the previous step Evaluate the solution. Is the problem solved correctly? Is this solution applicable to other problems? © 2006 Prentice-Hall, Inc.

The programming process can also be described as another four-step process, although in practice these steps often overlap: Define the problem Devise, refine, and test the algorithm Write the program Test and debug the program © 2006Prentice-Hall, Inc.

From Idea to Algorithm Start with a statement of the problem: A teacher needs a program that is 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 one 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. © 2006 Prentice-Hall, Inc.

Stepwise refinement Initially, a problem can be divided into three parts: a beginning, a middle, and an end Each of these parts represents a smaller programming problem to solve Begin Game Repeat Return until Number is Guessed End Game © 2006 Prentice-Hall, Inc.

The next refinement fills in a few details for each part: Begin Game Display instructions Pick a number between one and 100 Repeat Turn until Number is Guessed Input guess from user Respond to guess End repeat End Game Display end message © 2006 Prentice-Hall, Inc.

Control structures 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: choosing between alternative courses of action depending on certain conditions Repetition: allowing a group of steps to be repeated several times, usually until some condition is satisfied © 2006 Prentice-Hall, Inc.

display instructions pick a number between 1 and 100 set counter to 0 A sequence control structure if guess < number, then say guess is too small; else say guess is too big A selection control structure repeat turn until number is guessed or counter = 7 input guess from user add 1 to counter end repeat A repetition control structure © 2006 Prentice-Hall, Inc.

From Algorithm to Program A simple program contains: The program heading The declarations and definition The body The programmer defines the words number, guess, and counter Each of these words represents a variable—a named portion of the computer’s memory Variables become part of the program’s vocabulary Program can examine and change variables © 2006 Prentice-Hall, Inc.

Into the Computer A text editor is an application used to enter and save a program Either a translator or a compiler is used to translate a program into machine language Translation software (or a translator), called an interpreter, translates a high-level program to machine language one statement at a time during execution © 2006 Prentice-Hall, Inc.

Syntax errors—violations of the grammar rules of a programming language Often flagged automatically as soon as they’re typed into the editor Logic errors—problems with the logical structure of a program Cause differences between what the program is supposed to do and what it actually does Not always as easy to detect © 2006 Prentice-Hall, Inc.

A compiler translates an entire high-level program to machine language before executing the program A typical compiler is an integrated programming environment, containing A text editor A compiler A debugger to simplify the process of locating and correcting errors A variety of other programming utilities © 2006 Prentice-Hall, Inc.

Machine Language and Assembly Language
Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies Machine Language and Assembly Language Machine language: the native language of a computer Instructions for the four basic arithmetic operations, for comparing pairs of numbers, for repeating instructions, etc. are all binary Instructions, memory locations, numbers, and characters are all represented by strings of zeros and ones Assembly language: functionally equivalent to machine language but easier for people to read, write, and understand © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies
An assembler translates each statement of assembly language into a corresponding machine language statement © 2006 Prentice-Hall, Inc.

High-Level Languages High-level languages fall somewhere between natural human languages and precise machine languages Examples: C++, Java, Basic, FORTRAN, COBOL, Python, Pascal, LISP, ADA, PROLOG These languages are easier to write and debug and are transportable between machines © 2006 Prentice-Hall, Inc.

Structured Programming
Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies Structured Programming Structured programming is a technique that makes 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 © 2006 Prentice-Hall, Inc.

Object-Oriented Programming
Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies Object-Oriented Programming In object-oriented programming (OOP), a program is not just a collection of step-by-step instructions or procedures, but a collection of objects Objects contain both data and instructions and can send and receive messages C++ and Java are today’s most popular object-oriented languages © 2006 Prentice-Hall, Inc.

With OOP technology, programmers can build programs from prefabricated objects in the same way builders construct houses from prefabricated walls 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 © 2006 Prentice-Hall, Inc.

Visual Programming Visual programming tools enable programmers to create large portions of their programs by drawing pictures and pointing to on-screen objects Eliminates much of the tedious coding of traditional programming Apple’s HyperCard was probably the first popular example of a visual programming environment Includes a programming language called HyperTalk A HyperCard programmer doesn’t need to know HyperTalk to create working applications Microsoft’s Visual BASIC includes many of the ideas and tools of object-oriented programming © 2006 Prentice-Hall, Inc.

Languages for Users Macro languages (also called scripting languages) allow users to create programs, called macros, that automate repetitive tasks Microsoft Office includes a scripting variation of Visual Basic called Visual Basic for Applications (VBA) Fourth-generation languages (4GL) use English-like phrases and sentences to issue instructions Called nonprocedural languages Focus on what needs to be done, not how to do it One type of 4GL is the query language that enables a user to request information from a database SQL is the standard query language for most database applications today. © 2006 Prentice-Hall, Inc.

Component Software Component software makes it possible to construct small custom applications from software components The logical extension of object-oriented languages Customization is possible only if applications are programmed to allow it More and more software programs, including operating systems, are designed with extensibility in mind May soon reach a level where users and managers can build their own applications Web services (described in Chapters 10 and 15) are based on the idea of using components to create Web-centered systems and applications. © 2006 Prentice-Hall, Inc.

Extreme Programming Programmers use a variety of languages, including C and C++, to write Web applications Some programming languages are particularly useful for developing Web applications: HTML JavaScript Java Perl XML © 2006 Prentice-Hall, Inc.

Many experts see a future in which PC applications will take a backseat to Web-based applications Web-based personal information managers, reference tools, and games are growing steadily in popularity Because of the distributed nature of the Web and the limited bandwidth of many Internet connections, Web based applications present several challenges for users © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Systems Development Systems development: a problem-solving process of: Investigating a situation Designing a system solution to improve the situation Acquiring the resources to implement the solution Evaluating the success of the solution A steering committee may be formed to decide what projects should be considered first Made up of people from each functional area in the organization © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle A business organization may choose to contract, or outsource, a systems analyst from an outside consulting firm A systems analyst is an IT professional primarily responsible for developing and managing a system Avoids the need for permanent in-house staff Allows an organization to hire talent for selected activities on a contract basis End-user development allows end users to create applications End-users need access to and training in the use of Web site development tools, spreadsheet and database management packages, and fourth-generation languages © 2006 Prentice-Hall, Inc.

The Systems Development Life Cycle (SDLC)
Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Investigation The Systems Development Life Cycle (SDLC) The graphical “waterfall” model of the SDLC shows a basic sequential flow from identifying the “right things to do” to making sure that “things are done right” Analysis Design Development Implementation Maintenance Retirement © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems 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 © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems 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 © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Design Prototyping is an interactive methodology in which the prototype is continually modified and improved until it meets the needs of the end-user Identify requirements Develop working model of system Develop application, install prototype for evaluation by end-users, begin new prototype, or abandon application Make any necessary changes to prototype Use prototype Evaluate features of prototype © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Development The systems analyst must carefully plan and schedule activities in the development phase of the SDLC because they can overlap and occur simultaneously © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Implementation Direct cutover approach Parallel systems approach Phase-in approach Pilot approach © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Maintenance The maintenance phase involves monitoring, evaluating, repairing, and enhancing the system throughout the lifetime of the system © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems 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 © 2006 Prentice-Hall, Inc.

Systems Development Tools and Techniques
Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Systems Development Tools and Techniques Data collection techniques include: Review Interviews Questionnaires Observation Sampling © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Modeling tools Modeling tools are graphic representations of systems System flowcharts, data flow diagrams, data dictionaries, and decision tables are most widely-used © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Computer-aided systems engineering (CASE) tools include: Charting and diagramming tools to draw system flowcharts and data flow diagrams A centralized data dictionary containing detailed information about all the system components A user interface generator to create and evaluate many different interface designs Code generators that automate much of the computer programming to create a new system or application © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle Some CASE software packages contain tools that apply primarily to the analysis and design phases of the systems development life cycle Others contain tools that automate the later phases of systems development, implementation, and maintenance Integrated CASE tools incorporate the whole spectrum of tools to support the entire systems development life cycle © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Rules of Thumb
Avoiding Information Technology Project Failures Here are six tips for information workers on how to prevent the failure of IT projects: IT projects need executive sponsorship IT projects need user input IT projects need specifications IT projects need realistic expectations IT projects need cooperative business partners IT projects need open and honest communication © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 The Science of Computing
Many computer scientists prefer to call their 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 © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 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 © 2006 Prentice-Hall, Inc.

Software Solutions Computer scientists and software engineers are responding to reliability and cost problems on five main fronts: Programming techniques Programming environments Program verification Clean-room programming Human management It could well be that by the close of the twenty-first century, a new form of truly accessible programming will be the province of everyone, and will be viewed like writing, which was once the province of the ancient scribes but eventually became universally accessible. —Michael Dertouzos, in What Will Be © 2006 Prentice-Hall, Inc.

Software Warranties In the past, consumer software manufacturers provided no warranties for their products Today some manufacturers will give money back if the software cannot be installed on the computer No software manufacturer will accept liability for harm caused to you or your business by errors in software: Why? Additional precautions to make software work better would inflate cost and extend the time needed for development Only large companies would be able to sustain the pressure of such a scenario © 2006 Prentice-Hall, Inc.

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 Future programming tools will have little in common with today’s languages When future computer historians look back, they’ll marvel at how difficult it was for us to instruct computers to perform even the simplest actions © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Lesson Summary
Computer programming is a specialized form of problem solving that involves developing an algorithm for solving a problem Most programmers use stepwise refinement to repeatedly break a problem into smaller, more easily solvable problems Computer languages have evolved through several generations, with each generation easier to use and more powerful than the one that came before Most modern languages encourage structured programming © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Lesson Summary (continued)
Many applications contain built-in macro languages, scripting languages, and query languages that put programming power in the users Object-oriented programming (OOP) tools enable programmers to construct programs from objects with properties and provide the ability to send messages back and forth; many believe that OOP represents the future of programming Programs are part of larger information systems © 2006 Prentice-Hall, Inc.

Computer Confluence 7/e Chapter 14 Lesson Summary (continued)
Computer scientists are responsible for the software tools and concepts that make all other software development possible One of the most challenging problems facing computer science is the problem of software reliability As more and more human institutions rely on computer systems, it is becoming increasingly important for computer scientists to find ways to make software that people can trust © 2006 Prentice-Hall, Inc.

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