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Course Summary

Course Summary. Topics (1). Families of specification methods, evaluation criteria Safety and liveness Expressing properties in predicate calculus (logic) Input/output assertions, partial correctness, Hoare logic, invariants Z notations: dom ran and special symbols

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Course Summary

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  1. Course Summary

  2. Topics (1) • Families of specification methods, evaluation criteria • Safety and liveness • Expressing properties in predicate calculus (logic) • Input/output assertions, partial correctness, Hoare logic, invariants • Z notations: dom ran and special symbols • Z schemas: defining the state, operations • Z examples: symb. table, Unix files, telephone,...

  3. Topics (2) • Schema calculus: modularity, hiding,... • Refinement in Z: applying mapping functions, data and operation refinement, applicability and correctness • State machine: pure graph, traces, using Z for state machines • Statecharts: superstates, parallelism, joint transitions, history, micro-steps, activities • Temporal logics, linear: [], <>,..., next • Anchored version, past operators, classes of properties, fairness

  4. Topics (3) • Branching time: E, A, F, G, X, CTL • Real time: TIME, Zeno, ranges, bound vars. with temp. logic; for statecharts • Lamport’s textual state machines: open versus closed system, critical moment • Allowed changes, parameter passing • Fault tolerance, lossy queue and fairness, alternating bit protocol impl. of queue • Process algebras and LOTOS • Nondeterminism, gates, actions, • Process declaration and instantiation

  5. Topics (4) • Parallel comp.: |||, |[ gates ]|, | |, hiding • Offering (!) and accepting (?), negotiation • Stop, hiding, i, and multiway gates • Semantic views: bisimulation equivalence, testing equiv., trace equiv. • Algebraic specification and Larch, algebraic axioms, initial/final algebra • Generated by, partitioned by, converts • Shared versus Interface Languages

  6. Three kinds of specifications • Data and transition modeling: Z vrs. Larch shared lang.; For individual steps; textual, sequential • Control: Statecharts vrs. LOTOS (vrs. Esterelle vrs...) For concurrency, overlap, synchronization • Global liveness (and safety too): Temporal logic in some version

  7. Present Use of Formal Specifications • Invariants and I/O assertions: added to UML designs, appear as run-time checks, assert statements and checkers (in recent systems, around 10% of Microsoft code) • Elements of Z are in OCL (Object Constraint Language) extension of UML • Software model checkers Bandera, accepts Java programs annotated with a version of temporal logic SLAM, a Microsoft product for checking temporal logic assertions about driver software; now SDV Java Pathfinder: NASA tool for model checking Java

  8. Present use (cont.) • Feasibility checks for Java applets • No memory segment violations, no illegal operations • Legal requirements for formal specification and verification using a tool, in addition to testing • Aircraft control • Railway control in Europe and the US • Software controlling nuclear reactors in Europe • Description languages for test data generation • Hardware (design) verification using model checking and/or simulation: widely used in Intel, IBM, Motorola

  9. Trends • Use formal methods selectively for problem areas • Develop tools with clear added value • Use for error detection as well as showing correctness • Set up environment where methods can be combined (not yet widespread): • VeriTech: project to translate among verification tools and their specification notations • AOSD Formal Methods Lab: apply specification notations and verification tools to Aspect-Oriented Programming

  10. Realistically.... • Potential benefits are known. • Problems with formal methods have become evident. • Modeling and tools have helped on real projects in particular application areas. • Software development is in so much trouble, there is new willingness to invest in formal methods.

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