What Makes a Chain Longer?

• For software failure to occur, the following must occur:

  1. Execution- an input exercising the logical fault
  

2. Infection - the program fault corrupting the program's state, and

3. Propagation - the corrupt state propagating to the output

• Aside: POF = Pr[E] x Pr[I|E] x Pr[ P|I]

  (assuming one fault, otherwise, sum over all faults)
  

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