Software

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(No Transcript)
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Software
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How Programs Direct the CPU

• the typical CPU is designed to perform basic
  arithmetic, logic, and data transfer operations
• a program is a list of instructions that direct
  the processing of the computer
• programs are stored in memory and executed
  step-by-step by the CPU
• programs are translated to machine code for
  execution on a given processor

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Assembly Instruction Set
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A Simple Program
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Programming Language

• a tool for expressing computational processes
• a program is a list of statements in a
  programming language
• programs are symbolic representations of
  computational processes
• programs are translated to machine code for
  execution on a given processor

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Programming Languages

• ASSEMBLY LANGUAGES
• 11 representations of host processor machine
  code
• symbolic representations
• not portable
• Assembler translated code to machine language

• HIGH LEVEL LANGUAGES
• 1many representations of the machine code
• more abstract
• portable (with translation programs)
• Interpreter or Compiler translated code to
  machine language

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A Simple Program
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A Simple Program
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A Simple Program
FORTRAN DO 100 I 1, 10 PRINT
,I 100 CONTINUE
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A Simple Program
FORTRAN DO 100 I 1, 10 PRINT
,I 100 CONTINUE COBOL 100-PERFORM
200-PRINT-NUMBERS UNTIL COUNT IS EQUAL
10. 200-PRINT-NUMBERS ADD 1 TO
COUNT. WRITE COUNT TO DETAIL-LINE. WRITE
DETAIL-LINE AFTER ADVANCING 1 LINES
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A Simple Program
FORTRAN DO 100 I 1, 10 PRINT
,I 100 CONTINUE COBOL 100-PERFORM
200-PRINT-NUMBERS UNTIL COUNT IS EQUAL
10. 200-PRINT-NUMBERS ADD 1 TO
COUNT. WRITE COUNT TO DETAIL-LINE. WRITE
DETAIL-LINE AFTER ADVANCING 1
LINES BASIC 100 FOR I 1 TO 10 110
PRINT I 120 NEXT I
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Programming Paradigms

• A paradigm is a model of a process
• PROCEDURAL- The code specifies WHAT and HOW the
  processes is to be done
• NON-PROCEDURAL- the code specifies WHAT is to be
  done, but not HOW
• OBJECT ORIENTED- the data and code are together
  in units

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Programming Paradigms

• PROCEDURAL Program instructs the computer HOW
  to produce results.
• OPEN addressfile for reading
• WHILE NOT EOF DO
• READ first, last, address, city, state, zip
• IF last Massey THEN
• PRINT first, last
• ENDIF
• SKIP
• CLOSE addressfile

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Programming Paradigms

• NON PROCEDURAL The program has instructions
  WHAT is to be done, but not HOW it is to be done.
• SELECT first, last
• FROM addressfile
• WHERE last Massey
• ORDER by last, first
• SEND TO PRINTER

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Programming Paradigms

• OBJECT-ORIENTED contains both data and programs
  that operate on the data.
• Person object
• attributes of name, address, etc
• Methods of printing address, finding a name,
  sorting
• Employer object
• subclass of person
• addition attributes of parking space number,
  stock options
• additional methods of list members of department
  

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Visual Programming

• a method of using a GUI of predetermined objects
  to create the code automatically by manipulating
  graphical objects

Visual Programming allows programmers to write
programs by drawing pictures and pointing to
objects on the screen
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Software Complexity

• tasks that software systems model are often
  complicated and not well understood
• scale of software systems is often too great for
  a single person to comprehend and manage
• software systems components interact in
  unpredictable ways

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Risks of Software

• Mariner I Atlas booster fails (18 million)
• Mariner 8 probe lost
• Therac X-ray system kills two and injures others
• Over 1,000 British cancer patients are underdosed
  in radiation therapy
• Airbus 320 crashes due to control system problems
• Audi 5000 recalled after 250 accidents blamed on
  computer-controlled system malfunction
• ATT computer switching failure (1/15/90)

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How People Solve Problems
Problem solving involves

• Understanding the problem
• Devising a plan for solving the problem
• Carrying out the plan
• Evaluating the solution

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How People Make Programs
Programming involves

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

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Program Development Cycle

• ANALYSIS SPECIFICATION
• understanding the process or problem
• deciding on requirements and features

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Program Development Cycle

• DESIGN
• devising a plan
• dividing tasks into program components
• writing algorithms for program components

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Program Development Cycle

• CODING
• employing symbolic programming languages as an
  aid
• translating algorithms into executable programs

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Program Development Cycle

• TESTING CORRECTION
• assembling/testing program components
• testing the system
• maintenance revising the system to meet new
  specifications

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Software

• In house completed version is called
• Alpha version
• A complete version sent out to users to test
• Beta Version