12. Mission-Critical and Safety-Critical Systems

First, a simple question: should you bother to spend time reading this chapter (I'm sure there are many more exciting things to do)? Well, to answer that, ask yourself another simple, but very important, question. If your system misbehaves, what are the resulting consequences? User irritation, loss of work, loss of money, damage to equipment, injury to people, or death? These are just some possible outcomes. So, where is your system on this scale of things? Moreover, apart from the moral issues, what are the legal and financial consequences of such problems?

The purpose of this chapter is to help you to develop a design strategy for critical systems. It does this by doing the following:

• Explaining the meaning of critical and fault-tolerant systems
• Illustrating how systems may be classified in terms of the consequences of their failures
• Showing the relationship between failure severity levels, failure probabilities...