Static Safety Analysis of UML Action Semantics for Critical Systems Development

1
Static Safety Analysis of UML Action Semantics
for Critical Systems Development

• Zsigmond Pap, Dániel Varró

2
Summary

• Basic Safety criteria
• Action Semantics
• Safety Problems in Action Semantics
• Structural Model Extensions for Safety Analysis
• Static Safety Analysis Methods
• Conclusion

3
Basic Safety criteria

• Safety-critical system
• 47 Leveson-criteria for system safety
• Especially for Specification
• Natural language
• Indeterminism
• Incompleteness
• Inconsistency

4
Action Semantics
Old Version (UML 1.7) New Version (UML 2.0)
5
Safety Problems in Action Semantics
Inconsistency II.
Inconsistency I.
Action
Action2
Action1
Action
Action3
Shared variable
Incompleteness
Action1
Action1
Action3
Variable
Action5
Action2
Action2
Action4
6
Structural Model Extensions for Safety Analysis
Action1

• New association required
• Allowed parallelism

Parallel
Action2
Pos1
Pos1
Array
Pos2
Array
Pos2
p1.Read(p2)
p1.Read(p2)
p1.Read(p2)
p1.Read(p2)
1
2
1
2
p1.Write(p2,p3)
p1.Write(p2,p3)
p1.Write(p2,p3)
p1.Write(p2,p3)
3
4
3
4
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Static Safety Analysis Methods

• Find indeterminism, inconsistency,
  incompleteness
• Automatic checking
• Proofed method

Graph-transformation and verification.
Action1
Action1
Action1
a1
parallel
Action2
variable
a2
Action2
Action2
Action3
Inconsistency
Indeterminism
Incompleteness
8
Static Safety Analysis Methods
Graph-transformation and verification.
Left side
Right side
Action
Action
Fork
Action
Action
Parallel
Action
Action
Rule to convert Fork into a set of standard
elements.
A3
A1
A5
A3
A1
A5
Fork
Parallel
A4
A6
A2
A4
A6
A2
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Static Safety Analysis Methods
Transitivity
Left side
Right side
B
B
A
A
C
C
Rule to build the transitive closure of the
causal dependencies
10
Static Safety Analysis Methods
Matching samples
X
A2
A2
X
A1
A1
X
Incompleteness
Inconsistency
11
Conclusion

• Part of a broader environment State Charts
• No well-usable AS tools available yet (We used
  general tools)
• Successfully tested Fire-, intrusion- and gas-
  detection system
• Almost 40 errors found in a small project