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

Renate Ristov

Fachgebiet SoftwaretechnikProf. 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 SoftwaretechnikProf. Dr. Wilhelm SchäferMotivation

Intra-object behaviorInter-object behavior

?

Renate Ristov Synthesis of State Machines from LSCs - 3

Fachgebiet SoftwaretechnikProf. Dr. Wilhelm SchäferCoffee Vending Machine

Renate Ristov Synthesis of State Machines from LSCs - 4

Fachgebiet SoftwaretechnikProf. Dr. Wilhelm SchäferPlay-in/Play-out

Renate Ristov Synthesis of State Machines from LSCs - 5

Fachgebiet SoftwaretechnikProf. Dr. Wilhelm SchäferProblem 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 SoftwaretechnikProf. Dr. Wilhelm SchäferDeciding Consistency

DFA for every LSC

Product Automaton

Eliminating Bad States and Transitions

Renate Ristov Synthesis of State Machines from LSCs - 7

Fachgebiet SoftwaretechnikProf. Dr. Wilhelm SchäferNot Consistent Specification

Restricted messages: prep_coffee

Renate Ristov Synthesis of State Machines from LSCs - 8

Fachgebiet SoftwaretechnikProf. Dr. Wilhelm SchäferDFA for every LSC

All messages without insert_coin

All messages not in the chart and not prep_coffee

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Fachgebiet SoftwaretechnikProf. Dr. Wilhelm SchäferProduct Automaton

Renate Ristov Synthesis of State Machines from LSCs - 10

Fachgebiet SoftwaretechnikProf. 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 SoftwaretechnikProf. 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 SoftwaretechnikProf. 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 SoftwaretechnikProf. 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 SoftwaretechnikProf. 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 SoftwaretechnikProf. 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 SoftwaretechnikProf. 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 SoftwaretechnikProf. 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 SoftwaretechnikProf. Dr. Wilhelm Schäfer

Eliminating Bad States and Transitions

No object system found to satisfy the LSCs

LSC specification not consistent

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Fachgebiet SoftwaretechnikProf. Dr. Wilhelm SchäferCorrected Specification

Restricted messages: prep_coffee

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Fachgebiet SoftwaretechnikProf. Dr. Wilhelm SchäferGlobal System Automaton

Renate Ristov Synthesis of State Machines from LSCs - 21

Fachgebiet SoftwaretechnikProf. 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 SoftwaretechnikProf. Dr. Wilhelm SchäferDistributing 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 SoftwaretechnikProf. Dr. Wilhelm SchäferComplexity

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 SoftwaretechnikProf. Dr. Wilhelm SchäferDiscussion

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 SoftwaretechnikProf. Dr. Wilhelm SchäferAnother approach

Using smart play-out to find consistency Encode play-out in a transition system

(only one of many) Model Checking:

i i

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 SoftwaretechnikProf. Dr. Wilhelm SchäferSummary

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