- Redundancy
11.7) It has been suggested that the control software for radiation therapy machine, used to treat patients with cancer, should be implemented using N-version programming. Comment on whether or not you think this is a good decision.
- I think this would be a bad idea. and incorrect dose of radiation would be extremely dangerous to patient.
11.9) Explain why you should explicitly handle exceptions in a system that is intended to have a high level of availability.
- The more available a system is, the more it will be running. Exceptions need to be handled to ensure the entire system doesn't stop working unexpectedly.
12.5) A train protection system automatically applies the brakes of a train if the speed limit for a segment of track is exceeded, or if the train enters a track segment that is currently signaled with a red light(i.e., the segment should not be entered). There are two critical safety requirements for this train protection system:
The train shall not enter a segment of track that is signaled with a red light.
The train shall not exceed the specified speed limit for a section of track.
Assuming that the signal status and the speed limit for the track segment are transmitted to on-board software on the train before it enters the track segment, propose five possible functional system requirements for the onboard software that may be generated from the system safety requirements.
- If the next segment of track is red, apply the breaks.
- If the next segment of track is green and the allowed speed is higher, accelerate until speed matches the segment.
- If the next segment of track is green and the allowed speed is lower, apply breaks until speed matches the segment.
- If speed is higher than the current segment's allowed speed, apply breaks until speed is lower than the speed limit.
- If speed is lower than the current segment's speed limit, accelerate until the speed matches the speed limit.
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