#dependability
Removing or reducing the number of fault can be performed both during the development and operational life of a system.
Fault removal during development consists of three steps: verification, diagnosis, and correction.
Verification: Process of checking whether the system adheres to given properties (verification conditions). Verification steps can be classified based on how it exercises the system:
- Static verification does not involve actual execution.
- Dynamic verification is verification through exercising the system.
- If the input is symbolic, it is called symbolic execution.
- On the other hand, if actual inputs are used it is called testing. When faults or errors are a a part of the test pattern, the testing method involves fault injection.
Designing a system to facilitate its verification is called design for verifiability.
Diagnosis kicks in when there are faults that prevented the verification conditions from being fulfilled, and the necessary corrections are performed.
Fault removal during operational phase can be either corrective or preventive maintenance.
- Corrective maintenance aims to remove faults that have produced one or more errors and have been reported.
- Preventive maintenance is a preemptive measure to uncover and remove faults that could lead to errors.