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Review of topics

Review of topics. Final exam : May 2nd to May 7 th Projects due on May 7th. Modeling. Finite-state models (Kripke structures) Symbolic modeling of transition systems: Boolean variables Transitions described logically Semantics of the Kripke structure generated

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Review of topics

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  1. Review of topics Final exam : May 2nd to May 7th Projects due on May 7th

  2. Modeling • Finite-state models (Kripke structures) • Symbolic modeling of transition systems: • Boolean variables • Transitions described logically • Semantics of the Kripke structure generated • Modeling recursive Boolean programs

  3. Specification logics • Reachability: • Solving reachability explicitly (DFS/BFS) • Computation Tree Logic (CTL) • Syntax and semantics • Ability to write CTL specs given English spec • Ability to interpret CTL specs

  4. Symbolic approach • Boolean decision diagrams (BDDs) • The representation of a function using a BDD • BDD canonical given ordering • Importance of ordering variables • Operations on BDDs: • AND, OR, NOT • EXISTS

  5. Symbolic model-checking • Reachability algorithms using BDDs • Symbolic CTL model-checking • Using NuSMV to symbolically model-check reachability and CTL.

  6. Specification logics contd. • Automata on infinite words (Buchi automata) • Linear temporal logic • Converting linear temporal logic to Buchi Automata • Automata-theoretic method for model checking LTL

  7. Bounded model-checking • Formulating bounded model-checking as a SAT formula (encoding initial and final conditions, the transitions functions and k-step reachability)

  8. Dataflow analysis • Generic setup of dataflow problems • Set of dataflow facts and lattice • Flow functions • The maximal-fixpoint (MFP) and meet-over-all-paths (MOP) formulations • Kill-gen functions, distributive flows

  9. Dataflow Analysis • Lattices and fixed points • Tarski’s thm: existence of least fixed point for monotonic functions on a lattice • Difference between MFP and MOP • MFP = MOP for distributive flows

  10. Dataflow analysis • Chaotic iteration to solve MFP problems for lattices where there are no infinite ascending chains. • Automata-based analysis for MOP problems where the dataflow lattice is finite

  11. Reachability in pushdown systems • Games on finite graphs • Solving games using the attractor method • Reachability of pushdown systems • Reduction to games on finite graphs.

  12. Analysis of programs with function calls • Reducing interprocedural MOP analysis to reachability in pushdown systems

  13. Floyd’s framework of verification • Floyd’s framework • Notion of interpretations • Logic to express invariants • Checking pre-post invariants to establish safety properties • Using ranking functions to prove that programs terminate

  14. Preconditions and postconditions • Definition of strongest postconditions and weakest pre-conditions • Deriving the strongest post-condition for all standard operations (assignment, etc.) • Using existential quantification

  15. Preconditions and postconditions • Deriving the weakest pre-condition for all standard operations (assignment, etc.) • Without using existential quantification • (see Graf-Saidi) Equivalence: strongest-postcondition(P) => Q  P => weakest-precondition(Q)

  16. Proving programs correct • Ability to find invariants and prove programs correct using Floyd’s framework

  17. Predicate abstraction • Predicate abstraction • Building the abstract program using precondition checks • Ability to manually abstract a program with respect to a set of predicates (and hence prove a property) • No testing of formal notation of abstract interpretation

  18. Symbolic evaluation • Ability to write down the constraints to check feasibility of a control-path of a program • No formalisms; but must be able to do examples

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