Computer Confluence 7/e Chapter 14 Systems Design and Development

Computer Confluence 7/e

Computer Confluence 7/e

• Chapter 14

• Systems Design and Development

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

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

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

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

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?

Computer Confluence 7/e Chapter 14 How People Make Programs

• 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

Computer Confluence 7/e Chapter 14 How People Make Programs

• From Idea to Algorithm

• Start with a statement of the problem:

Computer Confluence 7/e Chapter 14 How People Make Programs

• 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

Computer Confluence 7/e Chapter 14 How People Make Programs

• The next refinement fills in a few details for each part:

Computer Confluence 7/e Chapter 14 How People Make Programs

• 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

Computer Confluence 7/e Chapter 14 How People Make Programs

Computer Confluence 7/e Chapter 14 How People Make Programs

• Testing the algorithm

• 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

Computer Confluence 7/e Chapter 14 How People Make Programs

• 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

Computer Confluence 7/e Chapter 14 How People Make Programs

• 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

Computer Confluence 7/e Chapter 14 How People Make Programs

• 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

Computer Confluence 7/e Chapter 14 How People Make Programs

• 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

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

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies

• An assembler translates each statement of assembly language into a corresponding machine language statement

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies

• 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

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

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

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies

• 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

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies

• 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

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies

• 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

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies

• 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

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies

• 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

Computer Confluence 7/e Chapter 14 Programming Languages and Methodologies

• 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

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

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

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle

Computer Confluence 7/e Chapter 14 Programs in Perspective: Systems Analysis and the Systems Life Cycle

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

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

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

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

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

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

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

Computer Confluence 7/e Chapter 14 The State of Software

• 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

Computer Confluence 7/e Chapter 14 The State of Software

• 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

Computer Confluence 7/e Chapter 14 The State of Software

• 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

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

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

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