Interacting Process Classes

1
Interacting Process Classes

• P.S. Thiagarajan
• National University of Singapore
• Joint with Ankit Goel, Abhik Roychoudhury, Sun
  Meng
• To be presented at ICSE 2006

2
Outline

• Many reactive systems consist of classes of
  active objects interacting with each other.
• Processes, agents
• Phones, trains, airplanes,
• Similar behaviors
• Take part in the same types of transactions.
• Play same types of roles in these transactions.

3
Goals

• Develop
• a modeling technique.
• Using familiar notations
• A symbolic simulation technique
• Time and space efficient
• Do not maintain a name space.
• Thousands of objects in a class.
• Dont want to fix the number of objects in a
  class.
• Symbolic verification techniques.

4
A Process
d
c
r
d
5
A Process
d
c
r
d
6
A Process
d
c
r
d
7
A Process
d
c
r
d
8
A Process Class (Multiple Instances)
d
c
r
d
9
A Process Class (Multiple Instances)
d
c
r
d
10
A Process Class (Multiple Instances)
d
c
r
d
11
A Process Class (Multiple Instances)
d
c
r
d
12
A Process Class (Multiple Instances)
d
c
r
d
13
A Process Class (Multiple Instances)
d
c
r
d
But the actions c, r, d, d can represent
transactions between different objects of the
same class.
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A Process Class (Multiple Instances)
c
r
TR1c
TR1r
TR1
15
A Process Class (Multiple Instances)
TR1c
c
r
TR1r
TR1
16
A Process Class (Multiple Instances)
TR1c
c
r
TR1r
TR1
17
A Process Class (Multiple Instances)
TR2d
TR1c
d
d
TR1r
TR2d
TR2
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Phone Class
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Switch Class
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Call
MSCs Depict Two way flow of information. Define
roles.
21
Call
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Interacting Process Classes

• Multiple process Classes
• Transactions
• Can involve multiple objects
• Belonging to the same class
• Belonging to different classes
• Will have guards
• Histories of the participating objects
• States of the participating objects
• Values of the variables of the objects.
• Static and dynamic associations.

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g2
g1
g3
(r1, C1)
g1 a regular expression over the local
actions (TR, role) of the transition system
of C1.
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?1
(r1, C1)
?1 A boolean predicate over the values of the
variables associated with the object in C1 chosen
to play the role r1.
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(r1, C1)
(r2, C2)
(x, y) in SAME_AREA
Local Call
Static associations capture the structural
constraints. Relations with fixed extensions.
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(x, y) in CONNECTED
Local Call
Dynamic Associations Established across
classes. Relations with changing extensions.
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(x, y) in CONNECTED
(x, y) not in CONNECTED
Disconnect
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Symbolic Simulation

• Do not maintain name spaces.
• Group the objects of a class into behavioral
  subclasses.
• Track only the number of objects in a behavioral
  subclass.
• When a transaction executes these counts will be
  updated
• Behavioral subclasses get split and merged.

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Symbolic simulation

• At a configuration, two objects belong to the
  same behavioral subclass iff
• They are in the same control location.
• Satisfy the same static and dynamic associations.
• Satisfy the same history predicates associated
  with the guards.
• Satisfy the same (boolean) predicates on the
  respective local variables.

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Symbolic simulation

• This is an (over) approximation.
• There may be spurious symbolic runs with no
  corresponding concrete runs.
• But one can check not efficiently!- whether a
  symbolic run corresponds to a concrete run.
• quite useful.

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Current Status

• Drastically cuts simulation time/memory for
  realistic controllers
• CTAS weather update controller
• Rail Shuttle system from Paderborn
• Benchmarks for State Seq. Diagram modeling
• Rail car (from LSCs)
• Telephone switch network (from SPIN)
• Simulator found realizable bugs in the examples

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The number of behavioral subclasses remain small.
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This is all very well in practice but What about
the theory?
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Current Issues

• Abstraction-based verification methods.
• Currently underway.
• What is a good first order temporal logic for
  this model?
• Will suffice to have an efficient model checking
  procedure.
• The non-logical vocabulary is fixed by the model.
• Interpretations only over finite sets.

35
A Specification Logic

• C(x) R(x, y)
• ? ? ? ? ?
• lttr(x, y, z)gt? ? UNTIL ?
• (?x) ?

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Conclusion

• Multiple active objects of a class interacting
  with each other is a useful modelling idea
• Other applications?
• Introduce stochastic dynamics.