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CS605 - Software Engineering II - Lecture Handout 31

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Software Safety

Software Safety is a software SQA activity that focuses on identification of potential hazards that may affect software negatively and cause an entire system to fail. Modeling and analysis process is conducted as part of software safety and hazards are identified and categorized by criticality and risk.


Let us assume that the following hazards are associated with a computer-based cruise control for an automobile:

  • Causes uncontrolled acceleration that cannot be stopped
  • Does not respond to depression of brake pedal
  • Does not engage when switch is activated
  • Slowly loses or gains speed

Once system-level hazards are identified, analysis techniques are used to assign severity, and probability of occurrence. This technique is similar to risk analysis. To be effective, software must be analyzed in the context of the entire system. Analysis techniques such as fault tree analysis can be used to predict the chain of events that can cause hazards and the probability that each of these events will occur to create the chain. Once hazards are identified and analyzed, safety-related requirements can be specified for the software.

Reliability and safety are closely related. Software reliability uses statistical techniques to determine the likelihood that a software failure will occur. Occurrence of a software failure does not necessarily result in a hazard or mishap. On the other hand, software safety examines the ways in which failures result in conditions that can lead to a mishap.