Why Software Engineering

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Why Software Engineering?
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What is software?

• A program and all of its associated information
  and materials needed to support its installation,
  operation, repair and enhancement.

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What is SE?(1)

• Solving Problems
• Analyzing
• Synthesis
• Method or Technique
• Tool
• Procedure
• Paradigm

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What is SE?(2)

• We can view the computers and programming
  languages as tools to be used in designing and
  implementing a solution to a problem.

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What is good software?(1)

• Consideration of Software quality in 3 ways
• The quality of the product
• The quality of the process
• The quality in the context of the business
  environment
• Software quality
• Conformance
• Correctness
• Reliability
• Safety

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What is good software?(2) - The quality of the
product

• In view of users
• Easy to learn and use
• External characteristics failure
• In view of designer and maintainer
• Internal characteristics faults in
  requirements, design, and code inspections

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Data commonality
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What is good software?(3)- The quality of Process

• Activities that affect the ultimate product
  quality
• The quality of the development and maintenance
  process
• Modeling the process

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What is good software?(4)- Software quality

• Correctness the extent to which a program
  satisfies its specification and fulfills the
  customer's mission objectives
• Reliability probability of failure-free
  operation of a computer program for a specified
  time in a specified environment.
• Safety Probability that the conditions that can
  lead to a mishap (hazards) do not occur

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What is good software(5)?-Software quality
factors
Portability Reusability Interoperability
Maintainability Flexibility Testability
Product Revision
Product Transition
Product Operation
Correctness Reliability Efficiency Integrity
Usability
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Who does software engineering?

• Customer One who is paying for the software
  system
• Developer One who is building the software
  system for the customer
• User One who will actually use the system
• Subcontractor Additional developer who build s
  subsystem and deliver to the developers to be
  included in the final product

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A system approach(1)

• System
• Objects
• Activities
• A descriptions of the relationships among
  entities and activities
• A definition of the boundary of the system
• Activity Something that happens in a system.
• Objects(Entities) The elements involved in the
  activities.

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A system approach(2) - Interrelated systems

• The boundary of a system What is within and
  without and what crosses the boundary.
• One system exists inside another system Focus
  on the smallest system at first
• Incremental development
• When building a system to replace an older
  version.
• Static and dynamic views of a system.

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Reporting system for data
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A engineering approach - Building a system

• Construction of the system follows understanding
  its nature.
• Activities in the development of software
• Requirements analysis and definition
• System design
• Program design
• Writing the programs
• Unit testing
• Integration testing
• System testing
• System delivery
• Maintenance

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Members of the development team

• Requirements analyst
• Designer
• Programmer
• Tester
• Customer
• Trainer
• Maintenance team
• Librarian
• Configuration management team

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ANALYST
DESIGNER
PROGRAMMER
SOFTWARE DEVELOPMENT STEPS
DEVELOPER ROLES
TESTER
TRAINER
MAINTENANCE
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How has software engineering changed?(1)-The
nature of change

• Multiple systems, network control, security, user
  interface presentation waterfall
  approach to development is no longer suitable.
• Change factors
• Criticality of time-to-market for commercial
  products
• Shifts in the economics of computing
• Availability of powerful desktop computing
• Extensive local and wide-area networking
• Availability and adoption of oo tech.
• Graphical user interfaces
• Unpredictability of the waterfall model of
  software development

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Factors influencing software engineering

• Types of application
• Software size
• Software requirements
• Production and Acquisition mode
• Hardware environment
• Number of users

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Summary

• Software engineering definition
• The systematic approach to the development,
  operation - IEEE Computer Society.
• Design, building, and maintaining large software
  systems - Ian Sommervile.
• Software definition
• Problems in engineering quality software
• Cost overruns
• Late delivery
• Inadequate performance
• Unreliability
• Difficulty in maintenance

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Unsuccessful case - An Investigation of the
Therac-25 accidents(IEEE Computer, Jul. 1993)

• A computerized radiation therapy machine
• 1983-1984 accident free operation
• 1985-1987 6 accidents
• Safety-critical software
• Software development practice was unsatisfactory
• A single developer with unknown background or
  experience, using PDP 11 assembly
• Little documentation on software requirements and
  test plan
• Quality of safety is questionable