504 research outputs found

    Refining SCJ Mission Specifications into Parallel Handler Designs

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    Safety-Critical Java (SCJ) is a recent technology that restricts the execution and memory model of Java in such a way that applications can be statically analysed and certified for their real-time properties and safe use of memory. Our interest is in the development of comprehensive and sound techniques for the formal specification, refinement, design, and implementation of SCJ programs, using a correct-by-construction approach. As part of this work, we present here an account of laws and patterns that are of general use for the refinement of SCJ mission specifications into designs of parallel handlers used in the SCJ programming paradigm. Our notation is a combination of languages from the Circus family, supporting state-rich reactive models with the addition of class objects and real-time properties. Our work is a first step to elicit laws of programming for SCJ and fits into a refinement strategy that we have developed previously to derive SCJ programs.Comment: In Proceedings Refine 2013, arXiv:1305.563

    Towards a UTP semantics for modelica

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    We describe our work on a UTP semantics for the dynamic systems modelling language Modelica. This is a language for modelling a system’s continuous behaviour using a combination of differential algebraic equations and an event-handling system. We develop a novel UTP theory of hybrid relations, inspired by Hybrid CSP and Duration Calculus, that is purely relational and provides uniform handling of continuous and discrete variables. This theory is mechanised in our Isabelle implementation of the UTP, Isabelle/UTP, with which we verify some algebraic properties. Finally, we show how a subset of Modelica models can be given semantics using our theory. When combined with the wealth of existing UTP theories for discrete system modelling, our work enables a sound approach to heterogeneous semantics for Cyber-Physical systems by leveraging the theory linking facilities of the UTP

    Unifying Theories of Reactive Design Contracts

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    Design-by-contract is an important technique for model-based design in which a composite system is specified by a collection of contracts that specify the behavioural assumptions and guarantees of each component. In this paper, we describe a unifying theory for reactive design contracts that provides the basis for modelling and verification of reactive systems. We provide a language for expression and composition of contracts that is supported by a rich calculational theory. In contrast with other semantic models in the literature, our theory of contracts allow us to specify both the evolution of state variables and the permissible interactions with the environment. Moreover, our model of interaction is abstract, and supports, for instance, discrete time, continuous time, and hybrid computational models. Being based in Unifying Theories of Programming (UTP), our theory can be composed with further computational theories to support semantics for multi-paradigm languages. Practical reasoning support is provided via our proof framework, Isabelle/UTP, including a proof tactic that reduces a conjecture about a reactive program to three predicates, symbolically characterising its assumptions and guarantees about intermediate and final observations. This allows us to verify programs with a large or infinite state space. Our work advances the state-of-the-art in semantics for reactive languages, description of their contractual specifications, and compositional verification

    Automating Verification of State Machines with Reactive Designs and Isabelle/UTP

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    State-machine based notations are ubiquitous in the description of component systems, particularly in the robotic domain. To ensure these systems are safe and predictable, formal verification techniques are important, and can be cost-effective if they are both automated and scalable. In this paper, we present a verification approach for a diagrammatic state machine language that utilises theorem proving and a denotational semantics based on Unifying Theories of Programming (UTP). We provide the necessary theory to underpin state machines (including induction theorems for iterative processes), mechanise an action language for states and transitions, and use these to formalise the semantics. We then describe the verification approach, which supports infinite state systems, and exemplify it with a fully automated deadlock-freedom check. The work has been mechanised in our proof tool, Isabelle/UTP, and so also illustrates the use of UTP to build practical verification tools.Comment: 18 pages, 16th Intl. Conf. on Formal Aspects of Component Software (FACS 2018), October 2018, Pohang, South Kore

    A UTP semantics for communicating processes with shared variables and its formal encoding in PVS

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    CSP# (communicating sequential programs) is a modelling language designed for specifying concurrent systems by integrating CSP-like compositional operators with sequential programs updating shared variables. In this work, we define an observation-oriented denotational semantics in an open environment for the CSP# language based on the UTP framework. To deal with shared variables, we lift traditional event-based traces into mixed traces which consist of state-event pairs for recording process behaviours. To capture all possible concurrency behaviours between action/channel-based communications and global shared variables, we construct a comprehensive set of rules on merging traces from processes which run in parallel/interleaving. We also define refinement to check process equivalence and present a set of algebraic laws which are established based on our denotational semantics. We further encode our proposed denotational semantics into the PVS theorem prover. The encoding not only ensures the semantic consistency, but also builds up a theoretic foundation for machine-assisted verification of CSP# specifications.Full Tex

    UTP By Example : Designs

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    Towards Verification of Cyber-Physical Systems with UTP and Isabelle/HOL

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    In this paper, we outline our vision for building verification tools for Cyber-Physical Systems based on Hoare and He’s Unifying Theories of Programming (UTP) and interactive proof technology in Isabelle/HOL. We describe our mechanisation and explain some of the design decisions that we have taken to get a convenient and smooth implementation. In particular, we describe our use of lenses to encode state. We illustrate our work with an example UTP theory and describe the implementation of three foundational theories: designs, reactive processes, and the hybrid relational calculus. We conclude by reflecting on how tools are linked by unifying theories
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