Automated study of failures Master Thesis. Cooperation between DoCS/ASTEC (Parosh A. Abdulla) And Prover Technology/ESACS (Ove Åkerlund)

ESACS Enhanced Safety Assessment for Complex Systems Members are from the aircraft industry … … and companies involved in formal methods (ex: Prover Technology)

Traditional development cycle Informal specification Implementation Tests

Safer development cycle Informal specification Implementation (model) Automated verification Formal specification

Failures Failures (i.e. hardware failures) are usually not taken into account Techniques exist: FTA (Fault Tree Analysis) Fault trees are still generated by hand Fault trees of system using software can be very large

FTA: Faults ignored Lamp Switch_on Light_emitted

FTA: addition of identified faults Lamp Switch_on Button Power_fail Bulb_fail Button_off_fail

FTA: Model with faults Lamp Switch_on Button Power_fail Bulb_fail Button_off_fail & Light_emitted 11

FTA: The tree Switch_on AND not Light_emitted 11 Power_failBulb_fail

FTA: The tree Not Switch_on AND Light_emitted & Not Power_failNot Bulb_failButton_off_fail

Difficulties Qualitative analysis –Find Minimum Prime Implicants –Problem is NP-Complete Quantitative analysis –Given probabilities of occurrence of basic failures, –Find the probabilities of occurrence of top events

Qualitative Analysis Prime Implicant –Assignment of values to variables –The restriction of a Boolean function by a Prime Implicant is always true –They represent ”causes” of top events –Can be used to speed up the quantitative analysis