A safety-critical software system for treating cancer patients has two principal components:

■ A radiation therapy machine that delivers controlled doses of radiation to tumour sites.

This machine is controlled by an embedded software system.

■ A treatment database that includes details of the treatment given to each patient.
Treatment requirements are entered in this database and are automatically downloaded to the radiation therapy machine.
Identify three hazards that may arise in this system. For each hazard, suggest a defensive requirement that will reduce the probability that these hazards will result in an accident.
Explain why your suggested defence is likely to reduce the risk associated with the hazard.