Alvaro Miyazawa

Features of CML: A formal modelling language for Systems of Systems

We discuss the initial design for CML, the first formal language specifically designed for modelling and analysing Systems of Systems (SoSs). It is presented through the use of an example: an SoS of independent telephone exchanges. Its overall behaviour is first specified as a communicating process: a centralised telephone exchange. This description is then refined into a network of telephone exchanges, each handling a partition of the set of subscribers (telephone users). The refinement is motivated by a non-functional requirement to minimise the cabling required to connect geographically distributed subscribers, who are clustered. The exchanges remain as independent systems with respect to their local subscribers, whose service is unaffected by the loss of remote exchanges.

COMPASS tool vision for a system of systems Collaborative Development Environment

It would be useful to have a tool platform that supports systematic engineering of Systems of Systems, especially focused on the case where multiple parties are collaborating on the development. We attempt to provide a vision for a tool that allows collaboration on models developed jointly and that can be systematically analysed. The focus is on the challenges that make this kind of tool - a Collaborative Development Environment- different from a traditional Integrated Development Environment. Finally the paper describes the plans of the COMPASS project to address these challenges.

SysML contracts for systems of systems

This paper proposes and demonstrates an architectural pattern for the contractual specification of interfaces between constituent systems within a System of Systems (SoS). We take a structured approach to the development of the pattern, which we call the Contract Pattern. It is developed and demonstrated in SysML using a case study from the Audio/Video domain. We also identify some of the obstacles in the way of checking the conformance of a constituent system to a contract, and discuss how these may be overcome.

Refinement-oriented models of Stateflow charts

Simulink block diagrams are widely used in industry for specifying control systems, and of particular interest and complexity are Stateflow blocks, which are themselves defined by separate charts. To make formal reasoning about diagrams and charts possible, we need to formalise their semantics; for the formal verification of their implementations, a refinement-based semantics is appropriate. An extensive subset of Simulink has been formalised in a language for refinement, namely, Circus, and here, we propose an approach to cover Stateflow charts. Our models are distinctive in their operational nature, which closely reflects the informal description of the Stateflow (simulation) semantics. We describe, formalise, and automate a strategy to generate our Circus models. The result is a solid foundation for reasoning based on refinement.

An Approach for Managing Semantic Heterogeneity in Systems of Systems Engineering

Semantic heterogeneity is a significant challenge to integration in Systems of Systems Engineering (SoSE) due the large variety of languages, domains and tools which are used in their construction. In this paper we envision a strategy for managing this heterogeneity by decomposing domain specific languages into their “building block” theories which can be independently analysed, and used as a basis for linking with similar notations. This provides a systematic approach to building a tool-chain which integrates the different theories, methods and tools used in SoSE. Our approach has been piloted on the development of theories enabling machine-supported analysis of SysML models of SoSs. We conclude that the approach has further potential and identify lines of future research, notably in techniques for handling mixed discrete and continuous behaviour, timebands, mobility and model integration in SoSE.

Formal Models of SysML Blocks

In this paper, we propose a formalisation of SysML blocks based on a state-rich process algebra that supports refinement, namely, CML. We first establish a set of guidelines of usage of SysML block definition and internal block diagrams. Next, we propose a formal semantics of SysML blocks described by diagrams that conform to our guidelines. The semantics is specified by inductive functions over the structure of SysML models. These functions can be mechanised to support automatic generation of the CML models.

Modelling and Verification for Swarm Robotics

RoboChart is a graphical domain-specific language, based on UML, but tailored for the modelling and verification of single robot systems. In this paper, we introduce RoboChart facilities for modelling and verifying heterogeneous collections of interacting robots. We propose a new construct that describes the collection itself, and a new communication construct that allows fine-grained control over the communication patterns of the robots. Using these novel constructs, we apply RoboChart to model a simple yet powerful and widely used algorithm to maintain the aggregation of a swarm. Our constructs can be useful also in the context of other diagrammatic languages, including UML, to describe collections of arbitrary interacting entities.

Modelling and Verification of Timed Robotic Controllers

Designing robotic systems can be very challenging, yet controllers are often specified using informal notations with development driven primarily by simulations and physical experiments, without relation to abstract models of requirements. The ability to perform formal analysis and replicate results across different robotic platforms is hindered by the lack of well-defined formal notations. In this paper we present a timed state-machine based formal notation for robotics that is informed by current practice. We motivate our work with an example from swarm robotics and define a compositional CSP-based discrete timed semantics suitable for refinement. Our results support verification and, importantly, enable rigorous connection with sound simulations and deployments.

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.

Formal Refinement in SysML

SysML is a UML-based graphical notation for systems engineering that is becoming a de facto standard. Whilst it reuses a number of UML diagrams, it introduces new diagrams, and maintains the loose UML semantics. Refinement is a formal technique that supports the validation and verification of models by capturing a notion of correctness based on observable behaviour. In this paper, we analyse the issue of formal refinement in the context of SysML. First, we identify the requirements for supporting refinement in SysML, next we propose extensions to SysML that satisfy these requirements, and finally we present a few refinement laws and discuss their validity.