Ex 11.4
Q: What is the common characteristic of all architectural styles that are geared to supporting software fault tolerance?
A: The system has to include redundant and diverse hardware and software. One of the simpler solutions is in replicated servers like what cloud providers use.
Ex 11.7
Q: It has been suggested that the control software for a reaction 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 suggestion.
A: I think this is a bad suggestion as N-version programming is based on 2 or more versions being the same and 1 not. When it comes to cancer therapy I feel like this is such a delicate topic that there should be more care going into the decisions made. Maybe even if 2 versions are not the same patient may have a special case where the unique output may be the best option for them. For this reason I do not think it is the best suggestions for reaction therapy machines.
Ex 11.9
Q: Explain why you should explicitly handle all exceptions in a system that is intended to have a high level of availability.
A: If it has a high level of availability, in order to maintain its efficiency it would need to be able to handle all exceptions.
Ex 12.5
Q: A train protection system automatically applied the brakes of the 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. There are 2 critical-safety requirements for this train protection system.
1. The train shall not enter a segment of track that is signaled with a red light.
2. 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 5 possible functional system requirements for the onboard software that may be generated from the system safety requirements.
A:
1. There should be a way for the conductor to overpower the machine if it malfunctions and says the track is green but it is actually red
2. There should be a way for the conductor to overpower the machine if it malfunctions and says it is not exceeding the speed limit when the conductor knows it is
3. There should be a way for the conductor to overpower the machine if it malfunctions and says it is exceeding the speed limit when the conductor knows it is not to maintain the flow of traffic efficiently
4. If the train is exceeding the speed limit the track should turn red until the speed limit is obeyed
5. A program should monitor all trains to prevent future collisions
Collaborated with Chandler Long
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