Computer Science 1JC3: Introduction to Computational Thinking

Lecture on Software Development

Introduction

• Course: Computer Science 1JC3
• Topic: Software Development - the last topic of the course.

Color Models in Art and Technology

• RGB Model: Used for producing color with light.
• CMY/CMYK Model: Used for producing color with ink.
• Traditional Artist Color Model: Red, Yellow, Blue
  • Creates intermediate colors: Orange, Green, Violet
• Historical models used by artists include:
  • Red-Yellow-Blue
  • Orange-Green-Violet

Analog Computing Devices

• Charles Babbage's Analytical Engine: Digital, mechanical engineering-based.
• Leibniz's Stoffelwalze: Digital.
• Abacus: Digital.
• Slide Rule: An analog computing device.
  • Used for computation by adding logarithms (equivalent to multiplication).
  • Transition away from slide rules in 1970s due to affordable electronic calculators.
  • Requires estimation skills due to lack of decimal point placement.

Case Study: Therac-25 Disaster

• A radiation therapy machine that caused harm due to software issues.
• Developed by Atomic Energy of Canada Limited (AECL).
• Incidents in the 1980s resulted in severe physical damage or death.
  • Example incident in Hamilton, Ontario.
• Causes of Failure:
  • Inadequate software design and development.
  • Coding and testing by one person.
  • No independent code review.
  • Poor documentation of error codes.
  • Missed race conditions and arithmetic overflow.
  • Poor user interface leading to input errors.
  • Software ignored in reliability modeling.
  • Lack of hardware interlocks.
• Emphasizes the importance of rational software development processes.

Challenges in Software Development

• Human errors are inevitable; processes should minimize and catch them.
• Imperfect communication between humans.
• Initial project uncertainties.
• Technological limitations.
• Changing requirements over time.

David Parnas

• Key figure in software engineering.
• Positions & Contributions:
  • Professor Emeritus at McMaster University.
  • Started the software engineering program at McMaster.
  • Developed ideas on information hiding and modular design.
  • Advocated for precise documentation, including Parnas tables.
  • Promoted software engineering as an engineering discipline.
  • Main influencer behind McMaster's undergraduate software engineering program.

Conclusion

• Importance of developing software through rational processes.
• Encouragement to read David Parnas's collected papers for deeper insights into software development challenges.