A short tutorial on model checking

1. Model Checking
Tutorial
By: Anit Thapaliya

2. Background
• System Verification: Checks whether
system fulfils the specifications that have
been identified.
– Verification: Are we building the product
right.
– Validation: Are we building the right product.

3. Formal Methods
Applied mathematics for modelling and
analysing of computer systems.
Formal Verification:
– Act of proving or disproving the correctness
of intended algorithms.
– Formal methods of mathematics based on
formal specification of system or property.

4. Techniques:
• Verification methods to check whether
the system description satisfy the
specification.

5. Approaches:
• Proof Based: trying to find out the proof
i.e. system description satisfy the
specification ( Г |- Ø)
– Deductive Method:
• Method: Provide a formal proof that p holds
• Tool: Proof Checker
• Applicable: if system has form a mathematic
theory.

6. Model Based
• Model Based: trying to compute whether
a model satisfy the specification (M ⊨ Ø)
– Methods: systematic check on P in all states
– Tool: SPIN, NuSMV
– Applicable if: System generate (Finite)
behavioural model.

7. Model Checking
• A successful approach of verifying
requirements.
• It is automatic, model based and property
verification approach.
• Used for concurrent and reactive system.
• Process satisfy system requirement (model)
and property (specification) of final system and
generate outputs “Yes” if satisfy or
counterexamples if not.

8. Linear Time Logic (LTL)
• It’s a temporary logic with connectives
that allow us to refer to the future.

9. LTC Syntax
• ϕ ::= ┴ | Τ | p | (¬ϕ) | (ϕ^ϕ) | (ϕvϕ) | (ϕ⇒ϕ) | (Xϕ) | (Fϕ) | (Gϕ) | (ϕUϕ) | (ϕWϕ) | (ϕRϕ)
Where is p is any propositional atom from the set Atom
┴ and Τ are the LTL formula as are all atom from Atom
¬ϕ are LTL formula if ϕ is one.
X,F,G,U,R and W are temporal connectives where
X = ‘neXT State’
F = Some future state
G = all future state (Globally)
U, R and G = Until, Release and Weak Until respectively.

10. Computational Tree Logic (CTL)
• It’s a branching time logic such as a
model of time in tree like structure
where future is not determined.

11. CTL Syntax
• ϕ ::= ┴ | Τ | p | (¬ϕ) | (ϕ^ϕ) | (ϕvϕ) | (ϕ⇒ϕ) | (AXϕ) | (EXϕ) | (AFϕ) | (EFϕ) | (AGϕ) |
(EGϕ) | A(ϕUϕ) | E(ϕUϕ)
Where is p ranges over a set of Atomic formulas.
A = Always or along all path
E = Exist or along at least one path
┴ and Τ are the LTL formula as are all atom from Atom
¬ϕ are LTL formula if ϕ is one.
X,F,G,U,R and W are temporal connectives where
X = ‘neXT State’
F = Some future state
G = all future state (Globally)
U, R and G = Until, Release and Weak Until respectively.

12. NuSMV
• NuSMV (New Symbolic Model Verifier)
model checking system
• It checks the validity of LTL and CTL
formulas on those models.
• SMV provides result Yes if the
specification satisfy the models or
counterexamples otherwise.

13. Thank You !!!