SCJ-Circus: specification and refinement of Safety-Critical Java programs

Safety-Critical Java (SCJ) is a version of Java for real-time, embedded, safety-critical applications. It supports certification via abstractions that enforce a particular program architecture, with controlled concurrency and memory models. SCJ is an Open Group standard, with a reference implementation, but little support for reasoning. Here, we present SCJ-Circus, a refinement notation for specification and verification of low-level models of SCJ programs. SCJ-Circus is part of the Circus family of state-rich process algebras: it includes the Circus constructs for modelling of sequential and concurrent behaviour based on Z and CSP, and the real-time and object-oriented extensions of Circus, in addition to the SCJ abstractions. We present the syntax of SCJ-Circus and its semantics, defined by mapping SCJ-Circus constructs to those of Circus. We also detail a refinement strategy that takes a Circus design that adheres to a multiprocessor cyclic executive pattern and produces an SCJ program design, described in SCJ-Circus. Finally, we show how this refinement strategy can be extended for more complex program architectures

Formal mutation testing for Circus

International audienceContext: The demand from industry for more dependable and scalable test-development mechanisms has fostered the use of formal models to guide the generation of tests. Despite many advancements having been obtained with state-based models, such as Finite State Machines (FSMs) and Input/Output Transition Systems (IOTSs), more advanced formalisms are required to specify large, state-rich, concurrent systems. Circus, a state-rich process algebra combining Z, CSP and a refinement calculus, is suitable for this; however, deriving tests from such models is accordingly more challenging. Recently, a testing theory has been stated for Circus, allowing the verification of process refinement based on exhaustive test sets. Objective: We investigate fault-based testing for refinement from Circus specifications using mutation. We seek the benefits of such techniques in test-set quality assertion and fault-based test-case selection. We target results relevant not only for Circus, but to any process algebra for refinement that combines CSP with a data language. Method: We present a formal definition for fault-based test sets, extending the Circus testing theory, and an extensive study of mutation operators for Circus. Using these results, we propose an approach to generate tests to kill mutants. Finally, we explain how prototype tool support can be obtained with the implementation of a mutant generator, a translator from Circus to CSP, and a refinement checker for CSP, and with

SCJ-Circus : a refinement-oriented formal notation for Safety-Critical Java

Safety-Critical Java (SCJ) is a version of Java whose goal is to support the development of real-time, embedded, safety-critical software. In particular, SCJ supports certification of such software by introducing abstractions that enforce a simpler architecture, and simpler concurrency and memory models. In this paper, we present SCJ-Circus, a refinement-oriented formal notation that supports the specification and verification of low-level programming models that include the new abstractions introduced by SCJ. SCJ-Circus is part of the family of state-rich process algebra Circus, as such, SCJ-Circus includes the Circus constructs for modelling sequential and concurrent behaviour, real-time and object orientation. We present here the syntax and semantics of SCJ-Circus, which is defined by mapping SCJ-Circus constructs to those of standard Circus. This is based on an existing approach for modelling SCJ programs. We also extend an existing Circus-based refinement strategy that targets SCJ programs to account for the generation of SCJ-Circus models close to implementations in SCJ

Refining SCJ Mission Specifications into Parallel Handler Designs

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

Circus Models for Safety-Critical Java Programs

Safety-critical Java (SCJ) is a restriction of the real-time specification for Java to support the development and certification of safety-critical applications. The SCJ technology specification is the result of an international effort from industry and academia. In this paper, we present a formalization of the SCJ Level 1 execution model, formalize a translation strategy from SCJ into a refinement notation and describe a tool that largely automates the generation of the formal models. Our modelling language is part of the Circus family; at the core, we have Z, communicating sequential processes and Morgan’s calculus, but we also use object-oriented and timed constructs from the OhCircus and Circus Time variants. Our work is an essential ingredient for the development of refinement-based reasoning techniques for SCJ

A Sublinear Tester for Outerplanarity (and Other Forbidden Minors) With One-Sided Error

We consider one-sided error property testing of $\mathcal{F}$-minor freeness in bounded-degree graphs for any finite family of graphs $\mathcal{F}$ that contains a minor of $K_{2,k}$, the $k$-circus graph, or the $(k\times 2)$-grid for any $k\in\mathbb{N}$. This includes, for instance, testing whether a graph is outerplanar or a cactus graph. The query complexity of our algorithm in terms of the number of vertices in the graph, $n$, is $\tilde{O}(n^{2/3} / \epsilon^5)$. Czumaj et~al.\ showed that cycle-freeness and $C_k$-minor freeness can be tested with query complexity $\tilde{O}(\sqrt{n})$ by using random walks, and that testing $H$-minor freeness for any $H$ that contains a cycles requires $\Omega(\sqrt{n})$ queries. In contrast to these results, we analyze the structure of the graph and show that either we can find a subgraph of sublinear size that includes the forbidden minor $H$, or we can find a pair of disjoint subsets of vertices whose edge-cut is large, which induces an $H$-minor.Comment: extended to testing outerplanarity, full version of ICALP pape

A timeband framework for modelling real-time systems

Complex real-time systems must integrate physical processes with digital control, human operation and organisational structures. New scientific foundations are required for specifying, designing and implementing these systems. One key challenge is to cope with the wide range of time scales and dynamics inherent in such systems. To exploit the unique properties of time, with the aim of producing more dependable computer-based systems, it is desirable to explicitly identify distinct time bands in which the system is situated. Such a framework enables the temporal properties and associated dynamic behaviour of existing systems to be described and the requirements for new or modified systems to be specified. A system model based on a finite set of distinct time bands is motivated and developed in this paper