399 research outputs found

    Diagrammatic Languages and Formal Verification : A Tool-Based Approach

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    The importance of software correctness has been accentuated as a growing number of safety-critical systems have been developed relying on software operating these systems. One of the more prominent methods targeting the construction of a correct program is formal verification. Formal verification identifies a correct program as a program that satisfies its specification and is free of defects. While in theory formal verification guarantees a correct implementation with respect to the specification, applying formal verification techniques in practice has shown to be difficult and expensive. In response to these challenges, various support methods and tools have been suggested for all phases from program specification to proving the derived verification conditions. This thesis concerns practical verification methods applied to diagrammatic modeling languages. While diagrammatic languages are widely used in communicating system design (e.g., UML) and behavior (e.g., state charts), most formal verification platforms require the specification to be written in a textual specification language or in the mathematical language of an underlying logical framework. One exception is invariant-based programming, in which programs together with their specifications are drawn as invariant diagrams, a type of state transition diagram annotated with intermediate assertions (preconditions, postconditions, invariants). Even though the allowed program states—called situations—are described diagrammatically, the intermediate assertions defining a situation’s meaning in the domain of the program are still written in conventional textual form. To explore the use of diagrams in expressing the intermediate assertions of invariant diagrams, we designed a pictorial language for expressing array properties. We further developed this notation into a diagrammatic domain-specific language (DSL) and implemented it as an extension to the Why3 platform. The DSL supports expression of array properties. The language is based on Reynolds’s interval and partition diagrams and includes a construct for mapping array intervals to logic predicates. Automated verification of a program is attained by generating the verification conditions and proving that they are true. In practice, full proof automation is not possible except for trivial programs and verifying even simple properties can require significant effort both in specification and proof stages. An animation tool which supports run-time evaluation of the program statements and intermediate assertions given any user-defined input can support this process. In particular, an execution trace leading up to a failed assertion constitutes a refutation of a verification condition that requires immediate attention. As an extension to Socos, a verificion tool for invariant diagrams built on top of the PVS proof system, we have developed an execution model where program statements and assertions can be evaluated in a given program state. A program is represented by an abstract datatype encoding the program state, together with a small-step state transition function encoding the evaluation of a single statement. This allows the program’s runtime behavior to be formally inspected during verification. We also implement animation and interactive debugging support for Socos. The thesis also explores visualization of system development in the context of model decomposition in Event-B. Decomposing a software system becomes increasingly critical as the system grows larger, since the workload on the theorem provers must be distributed effectively. Decomposition techniques have been suggested in several verification platforms to split the models into smaller units, each having fewer verification conditions and therefore imposing a lighter load on automatic theorem provers. In this work, we have investigated a refinement-based decomposition technique that makes the development process more resilient to change in specification and allows parallel development of sub-models by a team. As part of the research, we evaluated the technique on a small case study, a simplified version of a landing gear system verification presented by Boniol and Wiels, within the Event-B specification language.Vikten av programvaras korrekthet har accentuerats dĂ„ ett vĂ€xande antal sĂ€kerhetskritiska system, vilka Ă€r beroende av programvaran som styr dessa, har utvecklas. En av de mer framtrĂ€dande metoderna som riktar in sig pĂ„ utveckling av korrekt programvara Ă€r formell verifiering. Inom formell verifiering avses med ett korrekt program ett program som uppfyller sina specifikationer och som Ă€r fritt frĂ„n defekter. Medan formell verifiering teoretiskt sett kan garantera ett korrekt program med avseende pĂ„ specifikationerna, har tillĂ€mpligheten av formella verifieringsmetod visat sig i praktiken vara svĂ„r och dyr. Till svar pĂ„ dessa utmaningar har ett stort antal olika stödmetoder och automatiseringsverktyg föreslagits för samtliga faser frĂ„n specifikationen till bevisningen av de hĂ€rledda korrekthetsvillkoren. Denna avhandling behandlar praktiska verifieringsmetoder applicerade pĂ„ diagrambaserade modelleringssprĂ„k. Medan diagrambaserade sprĂ„k ofta anvĂ€nds för kommunikation av programvarudesign (t.ex. UML) samt beteende (t.ex. tillstĂ„ndsdiagram), krĂ€ver de flesta verifieringsplattformar att specifikationen kodas medelst ett textuellt specifikationsspĂ„k eller i sprĂ„ket hos det underliggande logiska ramverket. Ett undantag Ă€r invariantbaserad programmering, inom vilken ett program tillsammans med dess specifikation ritas upp som sk. invariantdiagram, en typ av tillstĂ„ndstransitionsdiagram annoterade med mellanliggande logiska villkor (förvillkor, eftervillkor, invarianter). Även om de tillĂ„tna programtillstĂ„nden—sk. situationer—beskrivs diagrammatiskt Ă€r de logiska predikaten som beskriver en situations betydelse i programmets domĂ€n fortfarande skriven pĂ„ konventionell textuell form. För att vidare undersöka anvĂ€ndningen av diagram vid beskrivningen av mellanliggande villkor inom invariantbaserad programming, har vi konstruerat ett bildbaserat sprĂ„k för villkor över arrayer. Vi har dĂ€refter vidareutvecklat detta sprĂ„k till ett diagrambaserat domĂ€n-specifikt sprĂ„k (domain-specific language, DSL) och implementerat stöd för det i verifieringsplattformen Why3. SprĂ„ket lĂ„ter anvĂ€ndaren uttrycka egenskaper hos arrayer, och Ă€r baserat pĂ„ Reynolds intevall- och partitionsdiagram samt inbegriper en konstruktion för mappning av array-intervall till logiska predikat. Automatisk verifiering av ett program uppnĂ„s genom generering av korrekthetsvillkor och Ă„tföljande bevisning av dessa. I praktiken kan full automatisering av bevis inte uppnĂ„s utom för trivial program, och Ă€ven bevisning av enkla egenskaper kan krĂ€va betydande anstrĂ€ngningar bĂ„de vid specifikations- och bevisfaserna. Ett animeringsverktyg som stöder exekvering av sĂ„vĂ€l programmets satser som mellanliggande villkor för godtycklig anvĂ€ndarinput kan vara till hjĂ€lp i denna process. SĂ€rskilt ett exekveringspĂ„r som leder upp till ett falskt mellanliggande villkor utgör ett direkt vederlĂ€ggande (refutation) av ett bevisvillkor, vilket krĂ€ver omedelbar uppmĂ€rksamhet frĂ„n programmeraren. Som ett tillĂ€gg till Socos, ett verifieringsverktyg för invariantdiagram baserat pĂ„ bevissystemet PVS, har vi utvecklat en exekveringsmodell dĂ€r programmets satser och villkor kan evalueras i ett givet programtillstĂ„nd. Ett program representeras av en abstrakt datatyp för programmets tillstĂ„nd tillsammans med en small-step transitionsfunktion för evalueringen av en enskild programsats. Detta möjliggör att ett programs exekvering formellt kan analyseras under verifieringen. Vi har ocksĂ„ implementerat animation och interaktiv felsökning i Socos. Avhandlingen undersöker ocksĂ„ visualisering av systemutveckling i samband med modelluppdelning inom Event-B. Uppdelning av en systemmodell blir allt mer kritisk dĂ„ ett systemet vĂ€xer sig större, emedan belastningen pĂ„ underliggande teorembe visare mĂ„ste fördelas effektivt. Uppdelningstekniker har föreslagits inom mĂ„nga olika verifieringsplattformar för att dela in modellerna i mindre enheter, sĂ„ att varje enhet har fĂ€rre verifieringsvillkor och dĂ€rmed innebĂ€r en mindre belastning pĂ„ de automatiska teorembevisarna. I detta arbete har vi undersökt en refinement-baserad uppdelningsteknik som gör utvecklingsprocessen mer kapabel att hantera förĂ€ndringar hos specifikationen och som tillĂ„ter parallell utveckling av delmodellerna inom ett team. Som en del av forskningen har vi utvĂ€rderat tekniken pĂ„ en liten fallstudie: en förenklad modell av automationen hos ett landningsstĂ€ll av Boniol and Wiels, uttryckt i Event-B-specifikationsprĂ„ket

    Formal Verification in the Loop to Enhance Verification of Safety-Critical Cyber-physical Systems

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    Formal verification may play a central role in the development of safecontrollers, such as those found in electric drives or (semi-)autonomousvehicles, whose complexity arises from the coexistence ofmechanical and electrical subsystems with sophisticated electronic controllersthat must implement high-level control policies according to different drivingmodes, while optimizing several objectives, such as safety first and foremost,efficiency, and performance among others.  Model-driven development resorts tosimulation to assess how well the various requirements and constraints aresatisfied, but there is a growing awareness that more rigorous methods areneeded to achieve the required levels of safety.  This paper proposes aconceptual framework for the development of complex systems based on (i)higher-order logic specification, (ii) verification by theorem proving, and(iii) tight integration of verification with model-driven development andsimulation.  This framework addresses both digital and analog systems, asillustrated with some examples in different fields including implantablebiomedical systems, autonomous vehicles, and electric valve actuation

    Verification of Symmetry Detection using PVS

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    One of the major limitations of model checking is that of state-space explosion. Symmetry reduction is a method that has been successfully used to alleviate this problem for models of systems that consist of sets of identical components. In earlier work, we have introduced a specification language, Promela-Lite, which captures the essential features of Promela but has a fully defined semantics. We used hand proofs to show that a static symmetry detection technique developed for this language is sound, and suitable to be used in a symmetry reduction tool for SPIN. One of the criticisms often levelled at verification implementations, is that they have not been proved mechanically to be correct, i.e., no mechanical formal verification technique has been used to check the soundness of the approach. In this paper, we address this issue by mechanically verifying the correctness of the symmetry detection technique. We do this by embedding the syntax and semantics of Promela-Lite into the theorem prover PVS and using these embeddings to both check the consistency of syntax/semantics definitions, and interactively prove relevant theoretical properties

    Emerging trends proceedings of the 17th International Conference on Theorem Proving in Higher Order Logics: TPHOLs 2004

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    technical reportThis volume constitutes the proceedings of the Emerging Trends track of the 17th International Conference on Theorem Proving in Higher Order Logics (TPHOLs 2004) held September 14-17, 2004 in Park City, Utah, USA. The TPHOLs conference covers all aspects of theorem proving in higher order logics as well as related topics in theorem proving and verification. There were 42 papers submitted to TPHOLs 2004 in the full research cate- gory, each of which was refereed by at least 3 reviewers selected by the program committee. Of these submissions, 21 were accepted for presentation at the con- ference and publication in volume 3223 of Springer?s Lecture Notes in Computer Science series. In keeping with longstanding tradition, TPHOLs 2004 also offered a venue for the presentation of work in progress, where researchers invite discussion by means of a brief introductory talk and then discuss their work at a poster session. The work-in-progress papers are held in this volume, which is published as a 2004 technical report of the School of Computing at the University of Utah

    Michael John Caldwell Gordon (FRS 1994), 28 February 1948 -- 22 August 2017

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    Michael Gordon was a pioneer in the field of interactive theorem proving and hardware verification. In the 1970s, he had the vision of formally verifying system designs, proving their correctness using mathematics and logic. He demonstrated his ideas on real-world computer designs. His students extended the work to such diverse areas as the verification of floating-point algorithms, the verification of probabilistic algorithms and the verified translation of source code to correct machine code. He was elected to the Royal Society in 1994, and he continued to produce outstanding research until retirement. His achievements include his work at Edinburgh University helping to create Edinburgh LCF, the first interactive theorem prover of its kind, and the ML family of functional programming languages. He adopted higher-order logic as a general formalism for verification, showing that it could specify hardware designs from the gate level right up to the processor level. It turned out to be an ideal formalism for many problems in computer science and mathematics. His tools and techniques have exerted a huge influence across the field of formal verification

    Abstract State Machines 1988-1998: Commented ASM Bibliography

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    An annotated bibliography of papers which deal with or use Abstract State Machines (ASMs), as of January 1998.Comment: Also maintained as a BibTeX file at http://www.eecs.umich.edu/gasm
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