A brief intro to Formal Methods modeling technique model checking. Also when and how to model.

1. Model checking
SANA RAHIM

2. -

3. Outline
o Background
o Current methods of verification
o Model checking
o Why model checking
o how to model

4. The Importance of Software Correctness
Defects can be fatal and extremely costly
 products subject to mass-production
 safety-critical systems

5. What is System Verification?
System verification amounts to check whether a system fulfills the
qualitative requirements that have been identified.
Software verification techniques:
 Peer reviewing
 Testing

6. Bug Hunting: the Sooner, the Better

7. Formal Verification Techniques
 Deductive methods
Formal proofs
 Model checking
systematic check in all states
tool: model checker (Spin, NuSMV, UppAal)
 Model-based simulation or testing
test by exploring possible behaviors

8. Model Checking
Model checking is a very effective technique to expose potential design
errors.
Or
Model checking is a formal verification technique based on graph
algorithms and formal logic. It allows the desired behavior (specification)
of a system to be verified, and its approach is to employ a suitable model
of the system

9. Why Model checking?
 Effective technique to identify potential design errors
 Widely used in the hardware and software fields
 Employed in the verification of microprocessors
 Security protocols
 Transportation sector (trains)
 Verification of software in the space sector.

11. What are Models?
 States labeled with basic propositions
 Transition relation between states
 Action-labeled transitions to facilitate composition

12. Transition system
A finite transition system is a mathematical description of the behavior of
systems, plants, controllers or environments with finite (discrete)
• inputs,
• outputs, and
• internal states and transitions between the states.

13. Transition system
A transition system is a tuple
Transition system = ( S, Act, →, S0 , AP, L)
Set of states a set of actions Initial state Labeling function
Atomic proposition
Transition

14. Atomic proposition
A proposition is a statement that can be either true or false, but not both.
An atomic proposition is one whose truth or falsity does not depend on the truth or falsity
of any other proposition.
Examples:
“Traffic light is green” is an atomic proposition”.
“If traffic light is green, the car can drive” is not an atomic proposition.

15. Labeling function
For state s, L(s) is the set of atomic propositions that are satisfied at s.
- Labels model outputs or observables.
- Actions model inputs or “communication.”

16. Example
S = {q0, q1}
Act = {rear, front, both, neither}
 = {(q0, front, q1),(q1, neither, q0),
(q1, rear, q1),...}
S0 = {q0}
L(q0) = {door is not open}
L(q1) = {door is open}