Subject: Software Engineering

Topic: Introduction to Software Engineering

Difficulty: High

There are three types of critical system:

Safety-critical systems A system whose failure may result in injury, loss of life or serious environmental damage. An example of a safety-critical system is a control system for a chemical manufacturing plant.

Mission-critical systems A system whose failure may result in the failure of some goal-directed activity. An example of a mission-critical system is a navigational system for a spacecraft.

Business-critical systems A system whose failure may result in very high costs for the business using that system. An example of a business-critical system is the customer accounting system in a bank.

The high costs of failure of critical systems means that trusted methods and techniques must be used for development. Consequently, critical systems are usually developed using well-tried techniques rather than newer techniques that have not been subject to extensive practical experience. They prefer to use older techniques whose strengths and weaknesses are understood, rather than new techniques which may appear to be better but whose long-term problems are unknown. Expensive software engineering techniques that are not cost-effective for non-critical systems may sometimes be used for critical systems development.