Computer Software

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CHAPTER 3

• Computer Software

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THE STORED PROGRAM CONCEPT

• COMPUTER IS A BINARY SYSTEM
• PROGRAM A set of instructions telling the
  computer what to do
• INSTRUCTION Individual step or operation in a
  program
• MACHINE LANGUAGE Translated instruction
  understood by particular model of computer

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EVOLUTION OF COMPUTER SOFTWARE

• FIRST GENERATION Machine language - binary
  language designed for particular computer
• SECOND GENERATION Assembly language -
  substituted mnemonic operation codes and
  addresses, translated to machine language by
  assembler

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EVOLUTION OF COMPUTER SOFTWARE

• THIRD GENERATION Procedural language - FORTRAN,
  COBOL, C - translated to machine language by
  compiler or interpreter. Example COBOL
• FOURTH GENERATION Nonprocedural language. Tell
  what to do, not how to do it, order not
  important. Translate to machine language by
  compiler or interpreter. Example FOCUS

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KEY TYPES OF SOFTWARE

• APPLICATION SOFTWARE Programs written to
  accomplish particular tasks for computer users
• SUPPORT SOFTWARE Programs that support
  application software in producing needed output.
  Does not directly produce output needed by users

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APPLICATION SOFTWARE

• WORD PROCESSING
• SPREADSHEETS
• DATABASE MANAGEMENT SYSTEMS
• PRESENTATION GRAPHICS

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APPLICATION SOFTWARE

• WORLD WIDE WEB BROWSERS
• ELECTRONIC MAIL, GROUPWARE
• DESKTOP PUBLISHING
• APPLICATION SUITES

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SUPPORT SOFTWARE

• OPERATING SYSTEMS Helps maximize work done,
  eases workload of users
• JOB CONTROL LANGUAGE Allows users to communicate
  with operating systems
• MULTIPROGRAMMING Large computers can run
  multiple programs simultaneously. Time-driven
  approach is time-sharing

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SUPPORT SOFTWARE

• MULTITASKING Allows small computers to work on
  several programs interactively
• VIRTUAL MEMORY Allows computer to run portions
  of a large program as required, saving use of
  main memory
• MULTIPROCESSING Multiple CPUs divide workload,
  increases efficiency

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SOURCES OF OPERATING SYSTEMS

• PROPRIETARY Written for particular computer
  class or system. Examples Windows 98, Windows
  2000
• OPEN SYSTEM Not tied to specific platform.
  Examples UNIX, Linux
• NETWORK OPERATING SYSTEM (NOS) Manages network
  resources, local area networks

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GRAPHICAL USER INTERFACE (GUI)

• MOUSE A standard pointing device
• ICON Graphic or label on screen associated with
  task or operation
• 32-BIT OPERATING SYSTEM Operating system handles
  32 bits at a time
• CLICKING MOUSE ON ICON INITIATES TASK

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OBJECT-ORIENTED PROGRAMMING (OOP)

• COMPUTER PROGRAMMING BASED ON CREATING, USING SET
  OF OBJECTS Object combines data and methods (or
  chunks of programs)
• EXAMPLES C, Smalltalk, Java

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OTHER LANGUAGES

• NATURAL LANGUAGES User types in or speaks
  English, computer evolves program
• HYPERTEXT MARKUP LANGUAGE (HTML) Code used to
  develop World Wide Web (WWW) pages and sites
• eXtensible Markup Language (XML) Used for data
  exchange on WWW

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DATABASE MANAGEMENT SYSTEM (DBMS)

• SUPPORT SOFTWARE USED TO CREATE, MANAGE, AND
  PROTECT ORGANIZATIONAL DATA
• DBMS Software that manages a database, works
  with operating system to store and modify data
  and to make data accessible in authorized ways

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TYPES OF DBMSs

• HIERARCHICAL Data arranged in a top-down,
  organization chart fashion
• NETWORK Data arranged like cities on a highway
  systems, often with multiple paths between pieces
  of data
• RELATIONAL Data arranged into simple tables, and
  records are related by storing common data in
  each of the associated tables

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FILING METHODS

• INDEXED SEQUENTIAL ACCESS METHOD (ISAM)
• EACH RECORD IDENTIFIED BY KEY
• GROUPED IN BLOCKS AND CYLINDERS
• KEYS IN INDEX
• VIRTUAL STORAGE ACCESS METHOD (VSAM)
• MEMORY DIVIDED INTO AREAS INTERVALS
• DYNAMIC FILE SPACE
• VSAM WIDELY USED FOR RELATIONAL DATABASES
• DIRECT FILE ACCESS METHOD

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COMPONENTS OF DBMS

• DATA DEFINITION LANGUAGE Defines data elements
  in database
• DATA MANIPULATION LANGUAGE Manipulates data for
  applications
• DATA DICTIONARY/DIRECTORY Formal definitions of
  all variables in database, controls variety of
  database contents

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STRUCTURED QUERY LANGUAGE (SQL)

• EMERGING STANDARD
• DATA MANIPULATION LANGUAGE
• FOR RELATIONAL DATABASES

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ADVANTAGES OF RELATIONAL DBMS

• NEW DATA ELEMENTS CAN EASILY BE ADDED AS NEW
  NEEDS ARISE
• NEW RELATIONSHIPS CAN BE CREATED AS NEW
  QUERY/REPORTING NEEDS CHANGE
• FEWER DATA CONSISTENCY PROBLEMS DUE TO LESS
  REDUNDANT DATA STORAGE
• MORE USER FRIENDLY TOOLS

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COMPUTER-AIDED SOFTWARE ENGINEERING (CASE)

• HELPS AUTOMATE SOFTWARE DEVELOPMENT Used by
  computer professionals to help automate software
  development
• MAY INCLUDE
• upper-CASE (requirements definition and design)
• lower-CASE (code generation)
• I-CASE or integrated-CASE

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CHANGING NATURE OF SOFTWARE

• MORE HARDWIRING OF SOFTWARE AND MORE MICROCODE
• MORE COMPLEXITY OF HARDWARE/SOFTWARE ARRANGEMENTS
• LESS CONCERN WITH MACHINE EFFICIENCY

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CHANGING NATURE OF SOFTWARE

• MORE PURCHASED APPLICATIONS AND MORE PORTABILITY
  OF THESE APPLICATIONS FROM ONE COMPUTER PLATFORM
  TO ANOTHER
• MORE PROGRAMMING USING OBJECT-ORIENTED AND VISUAL
  LANGUAGES, IN LARGE PART BECAUSE OF EMPHASIS ON
  GUIs

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CHANGING NATURE OF SOFTWARE

• MORE EMPHASIS ON APPLICATIONS THAT RUN ON
  INTRANETS AND THE INTERNET
• MORE USER DEVELOPMENT
• MORE USE OF PERSONAL PRODUCTIVITY SOFTWARE ON
  MICROCOMPUTERS, ESPECIALLY PACKAGES WITH A GUI

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CHAPTER 3

• Computer Software