Renate Ristov Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer 17. Juli 2008 Synthesizing State Machines from Live Sequence Charts Software Quality and Safety

Renate Ristov Synthesis of State Machines from LSCs - 2 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Motivation Intra-object behaviorInter-object behavior ?

Renate Ristov Synthesis of State Machines from LSCs - 3 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Coffee Vending Machine

Renate Ristov Synthesis of State Machines from LSCs - 4 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Play-in/Play-out

Renate Ristov Synthesis of State Machines from LSCs - 5 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Problem of Consistency Find an object system that satisfies the LSC specification: For every chart and every run, whenever the prechart holds the run must satisfy the chart LSC specification has to be consistent

Renate Ristov Synthesis of State Machines from LSCs - 6 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Deciding Consistency DFA for every LSC Product Automaton Eliminating Bad States and Transitions

Renate Ristov Synthesis of State Machines from LSCs - 7 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Not Consistent Specification Restricted messages: prep_coffee

Renate Ristov Synthesis of State Machines from LSCs - 8 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer DFA for every LSC All messages without insert_coin All messages not in the chart and not prep_coffee

Renate Ristov Synthesis of State Machines from LSCs - 9 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Product Automaton

Renate Ristov Synthesis of State Machines from LSCs - 10 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions DFA for every LSC Product Automaton Eliminating Bad States and Transitions

Renate Ristov Synthesis of State Machines from LSCs - 11 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions Bad Transition: System Messages from Accepting States

Renate Ristov Synthesis of State Machines from LSCs - 12 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions Bad Transition: System Messages from Accepting States

Renate Ristov Synthesis of State Machines from LSCs - 13 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions Bad Transition: System Messages from Accepting States Bad Transition: Environment Messages from Non-Accepting States

Renate Ristov Synthesis of State Machines from LSCs - 14 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions Bad Transition: System Messages from Accepting States Bad Transition: Environment Messages from Non-Accepting States

Renate Ristov Synthesis of State Machines from LSCs - 15 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions Bad Transition: System Messages from Accepting States Bad Transition: Environment Messages from Non- Accepting States Bad State: Accepting States, where Environment Message leads to Deadlock

Renate Ristov Synthesis of State Machines from LSCs - 16 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions Bad Transition: System Messages from Accepting States Bad Transition: Environment Messages from Non- Accepting States Bad State: Accepting States, where Environment Message leads to Deadlock

Renate Ristov Synthesis of State Machines from LSCs - 17 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions Bad Transition: System Messages from Accepting States Bad Transition: Environment Messages from Non- Accepting States Bad State: Accepting States, where Environment Message leads to Deadlock

Renate Ristov Synthesis of State Machines from LSCs - 18 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Eliminating Bad States and Transitions No object system found to satisfy the LSCs LSC specification not consistent

Renate Ristov Synthesis of State Machines from LSCs - 19 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Corrected Specification Restricted messages: prep_coffee

Renate Ristov Synthesis of State Machines from LSCs - 20 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Global System Automaton

Renate Ristov Synthesis of State Machines from LSCs - 21 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer DFA for every LSC Product Automaton Eliminating Bad States and Transitions Distributing the Global System Automaton Distributing the GSA

Renate Ristov Synthesis of State Machines from LSCs - 22 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Distributing the GSA Controller Object Controller Object in size of GSA Every Object size of 1 Full Duplication Every Object in size of GSA Partial Duplication Every Object size smaller than GSA But overall at least size of GSA

Renate Ristov Synthesis of State Machines from LSCs - 23 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Complexity Size of Global System Automaton (GSA) is dependent on size of LSC specification Size of LSC specification dependent Number of Objects Number of Charts Number of Messages Fix one number exponential in the size of other numbers Fix every number polynomial in the size of LSC specification Construction of GSA is polynomial in the size of GSA

Renate Ristov Synthesis of State Machines from LSCs - 24 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Discussion Very simple LSCs: No variables No conditions No complex constructs like alternatives, loops, etc. For large systems too much time and space needed to be practical

Renate Ristov Synthesis of State Machines from LSCs - 25 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Another approach Using smart play-out to find consistency Encode play-out in a transition system (only one of many) Model Checking: ii Technique not complete: Another transition system can be correct, but the algorithm did not find it LSCs have to be very detailed to bound the complexity (EF(AG( for all universal charts m (active m = 1)))

Renate Ristov Synthesis of State Machines from LSCs - 26 Fachgebiet Softwaretechnik Prof. Dr. Wilhelm Schäfer Summary Object System satisfies LSC specification iff LSC specification is consistent Very simple LSCs Not practical for large systems Another approach: Encoding with Smart Play-Out and Model Checking Richer LSCs Not complete DFA for every LSC Product Automaton Eliminating Bad States and Transitions Distributing the Global System Automaton