Homework #4 - 8/29 (Makeup)

Problem set:

11.4)

The project manager chose to use the sandwich testing method. This method is good for testing the top and bottom layers of the system in parallel. Also, there is no need to write test drivers or test stubs, since the actual system components in the top and bottom layers are being tested. The weakness of sandwich testing is that there is no unit tests for the target layer, in this case, layer II. The only times the middle layer components are tested is during the integration tests with the other subsystems.

11.7) Apply the software engineering and testing terminology from this chapter to the following terms used in Feynman's article mentioned in the introduction:

• What is a "crack"?
• What is "crack initiation"?
• What is "high engine reliability"?
• What is a "design aim"?
• What is a "mission equivalent"?
• What does "10 percent of the original specification" mean?
• How is Feynman using the term "vericfication," when he says that "As deficiencies and design errors are noted they are corrected and verified with further testing"?

• A "crack" in the turbine blade of the shuttle turbopump is called a "failure" in testing terminology. It is a deviation of the observed behavior from the specified behavior.
• "Crack initiation" is an erroneous state - continued operation will lead to a failure.
• Reliability is a measure of how the observed behavior compares to the specified behavior. High reliability means that the system performs how it was specified to. When he says "high engine reliability", he is talking about the engine performing as it was specified, with very low failure rate.
• The "design aim" is the desired reliability that is specified during the design phase of development.
• Again, the "mission equivalent" is the specified reliability. They wanted the engine to operate without failure for an amount of time that was equal to 55 missions, or "mission equivalent" of 55. In this case, that turned out to be 27,000 seconds of operation.
• This is talking about the observed reliability. Instead of being able to operate for a total of 55 missions without failure, some parts had to be replaced every 3 or 4 missions, and others every 5 or 6. This is where 10% comes from - on average, every 4 missions (4/55 ≈ 7%, which is why he said "at most, 10%") the engine had to be repaired.
• Feynman is describing "fault detection", which is the process of identifying erroneous states and their underlying faults. When he says the errors are "corrected and verified" he means the faults have been repaired and the new expected behavior has been tested again and proven to be sufficient.

*The homework states to do exercise 11.9, but there is no such problem listed in the back of the chapter.*