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CPSC 871
John D. McGregorModule 2 Session 2
Fault Analysis
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Fault/Failure
• A fault is a defect in a workproduct• A failure is a discrepancy from the expected
behavior at runtime.• Explicitly identifying what can go wrong and
designing for it is an important part of safety design.
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Fault Tree Analysis
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State machine for FHA
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Fault tolerant design
• We will expand on this later but in the context of understanding the problem:– The software product should be able to recognize failures– The software product should be able to either restart itself
or correct or notify user of the failure in a graceful manner (no blue screen of death)
• We will build as carefully as possible but fault tolerance allows the software to continue some level of operation in the presence of failures.
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Fault tolerance and domains
• What is an acceptable fault tolerant action varies from one domain to another.
• In aircraft, simply stopping the system is not an option while in robotic surgery stopping may be the safest option, not moving forward or backward.