Download SafEty and Risk Evaluation using bayesian NEts

SERENE Method Manual
Version 1.0 (F) May 1999
4.2.1 Reliability: Idiom Instances.......................................................................................................... 64
4.2.2 Building the Reliability Argument ................................................................................................ 67
4.2.3 Reliability: Execution Scenarios................................................................................................... 68
4.3 THE SAFETY RISK ARGUMENT ............................................................................................................... 70
4.3.1 Idiom Instances in the Safety Risk Template ................................................................................ 71
4.3.2 The Safety Risk Template.............................................................................................................. 72
4.3.3 The Satellite Templates in Safety Risk Argument ......................................................................... 72
4.3.4 Creating the Safety Risk Argument from Templates ..................................................................... 75
4.3.5 Safety Risk: Execution Scenario ................................................................................................... 76
5.
USING THE SERENE TOOL TO BUILD A BBN FROM IDIOMS ................................................. 80
5.1 BASIC FUNCTIONALITY OF THE TOOL ..................................................................................................... 80
5.2 DEFECTS EXAMPLE ................................................................................................................................ 84
5.2.1 Step 1: Create instantiation of the definition idiom...................................................................... 84
5.2.2 Step 2: Create an instantiation of the measurement idiom........................................................... 93
5.2.3 Step 3: Create instantiation of definition idiom: testing accuracy ............................................... 97
5.2.4 Step 4: Combining the templates .................................................................................................. 98
6.
REFERENCES ...................................................................................................................................... 104
7.
APPENDIX A: CONTEXT OF THE SERENE METHOD............................................................... 110
7.1 SAFETY DEVELOPMENT AND ASSESSMENT .......................................................................................... 110
7.2 SAFETY REGULATIONS AND STANDARDS ............................................................................................. 112
7.3 RISK ASSESSMENT................................................................................................................................ 114
7.4 SAFETY PRINCIPLES ............................................................................................................................. 115
7.4.1 Principles to determine acceptability of risk .............................................................................. 115
7.4.2 The ALARP Principle ................................................................................................................. 115
7.5 SAFETY LIFECYCLES ............................................................................................................................ 116
7.6 RELATIONSHIP TO SAFETY ANALYSIS TECHNIQUES ............................................................................. 117
7.6.1 Failure Analysis Techniques....................................................................................................... 117
7.6.2 Process Quality........................................................................................................................... 118
7.6.3 Metrics ........................................................................................................................................ 118
8.
APPENDIX B: FUNDAMENTALS OF PROBABILITY THEORY ............................................... 120
8.1 DIFFERENT APPROACHES TO PROBABILITY ........................................................................................... 120
8.1.1 Frequentist approach to probability........................................................................................... 120
8.1.2 Bayesian approach to probability .............................................................................................. 120
8.2 PROBABILITY AXIOMS .......................................................................................................................... 121
8.3 VARIABLES AND PROBABILITY DISTRIBUTIONS .................................................................................... 121
8.4 JOINT EVENTS AND MARGINALISATION ................................................................................................. 122
8.5 CONDITIONAL PROBABILITY ................................................................................................................. 123
8.6 BAYES THEOREM .................................................................................................................................. 123
8.6.1 Bayes Theorem Example............................................................................................................. 124
8.6.2 Likelihood Ratio ......................................................................................................................... 125
8.7 CHAIN RULE ......................................................................................................................................... 125
8.8 INDEPENDENCE AND CONDITIONAL INDEPENDENCE ............................................................................. 126
9.
APPENDIX C: BAYESIAN BELIEF NETS TUTORIAL................................................................. 128
9.1 DEFINITION OF BBNS: GRAPHS AND PROBABILITY TABLES .................................................................. 128
9.2 ANALYSING A BBN: ENTERING EVIDENCE AND PROPAGATION............................................................. 129
9.3 THE NOTION OF 'EXPLAINING AWAY' EVIDENCE .................................................................................... 130
9.4 WHY DO WE NEED A BBN FOR THE PROBABILITY COMPUTATIONS? ..................................................... 131
9.5 GENERAL CASE OF JOINT PROBABILITY DISTRIBUTION IN BBN ............................................................ 131
9.6 DEALING WITH THE INCREASES IN THE NUMBER OF VARIABLES ........................................................... 132
9.7 WHY WE SHOULD USE BBNS ................................................................................................................ 132
9.8 HOW BBNS DEAL WITH EVIDENCE ....................................................................................................... 132
9.8.1 Serial Connection ....................................................................................................................... 133
9.8.2 Diverging connection ................................................................................................................. 133
SERENE 22187 ESPRIT Framework IV Information Technology Programme Task 1.7
Page 6 of 200