Week 3 - Software Fault Tolerance

Question 1

What is a detector?

Answer 1

A class of program component that asserts the validity of a predicate in a running program

Question 2

What is a corrector?

Answer 2

A class of program that imposes a given predicate on a running program

Question 3

Give an example of a detector

Answer 3

Run time checks

Question 4

Give an example of a corrector

Answer 4

Exception handlers

Question 5

What is forward error recovery?

Answer 5

Upon detection of an error, program attempts to get into a state which is no longer erroneous

Question 6

What is backward error recovery?

Answer 6

Upon detection of an error program rolls back to a previously recorded good point

Question 7

What is a recovery line?

Answer 7

A recovery line is a set of checkpoints across all processes to which the programs can be rolled back

Question 8

What is N version programming?

Answer 8

The independent generation and utilisation of N functionally equivalent programs, where N >= 2. Typically uses majority voting for error detection.

Question 9

When does N version programming not work?

Answer 9

If all versions fail on the same inputs or in similar ways

Question 10

What is the coverage of dependability mechanisms?

Answer 10

The ratio of number of test cases successfully passed to the total number of test cases