Sequence Of Refinement Steps Research Articles

A tool-assisted method for the systematic construction of critical embedded systems using Event-B

Embedded control systems combine digital and physical components, leading to complex interactions and even complexity of their development. In [4] we proposed a method to build such complex systems in a systematic way. The overall method starts from an abstract model of the physical environment of the considered system and its controller. The method consists in a sequence of refinement steps, in the spirit of Event-B, that gradually introduces design details from an abstract level, until more concrete levels. Two main refinement processes are distinguished: one to capture the global model, the other to detail it; we provide through the method the guidelines to accompany these two refinement processes. But there were a lack of assistance tools. The designers need to be assisted by tools to guide them, to automate partially the refinements and to help in proving more easily model properties. We illustrate the method with the landing gear system case study and choosing the Event-B tool Rodin for illustration; we make it explicit the tools requirements for such a general method and, we introduce a tool support to assist the user in applying the method in combination with standard Event-B tool such as Rodin.

A Platform-Based Design Methodology With Contracts and Related Tools for the Design of Cyber-Physical Systems

We introduce a platform-based design methodology that uses contracts to specify and abstract the components of a cyber-physical system (CPS), and provide formal support to the entire CPS design flow. The design is carried out as a sequence of refinement steps from a high-level specification to an implementation built out of a library of components at the lower level. We review formalisms and tools that can be used to specify, analyze, or synthesize the design at different levels of abstraction. For each level, we highlight how the contract operations can be concretely computed as well as the research challenges that should be faced to fully implement them. We illustrate our approach on the design of embedded controllers for aircraft electric power distribution systems.

Methodology and Tools for Next Generation Cyber‐Physical Systems: The iCyPhy Approach

AbstractThe realization of complex, cyber‐physical “systems of systems” can substantially benefit from model‐based hierarchical and compositional methodologies to make their design possible let alone optimal. In this paper, we introduce the methodology being developed within the industrial Cyber‐Physical (iCyPhy) research consortium, which addresses the complexity and heterogeneity of cyber‐physical systems by formalizing the design process in a hierarchical and compositional way, and provides a unifying framework where different modeling, analysis and synthesis tools can seamlessly interconnect. We use assume‐guarantee contracts and their algebra (e.g. composition, conjunction, refinement) to provide formal support to the entire design flow. The design is carried out as a sequence of refinement steps from a high‐level specification (top‐down phase) to an implementation built out of a library of components at the lower level (bottom‐up phase). At each step, the design is refined by combining synthesis from requirements, optimization and simulation‐based design space exploration methods. We illustrate our approach on design examples of embedded controllers for aircraft power distribution and air management systems.

A Contract-Based Methodology for Aircraft Electric Power System Design

In an aircraft electric power system, one or more supervisory control units actuate a set of electromechanical switches to dynamically distribute power from generators to loads, while satisfying safety, reliability, and real-time performance requirements. To reduce expensive redesign steps, this control problem is generally addressed by minor incremental changes on top of consolidated solutions. A more systematic approach is hindered by a lack of rigorous design methodologies that allow estimating the impact of earlier design decisions on the final implementation. To achieve an optimal implementation that satisfies a set of requirements, we propose a platform-based methodology for electric power system design, which enables independent implementation of system topology (i.e., interconnection among elements) and control protocol by using a compositional approach. In our flow, design space exploration is carried out as a sequence of refinement steps from the initial specification toward a final implementation by mapping higher level behavioral and performance models into a set of either existing or virtual library components at the lower level of abstraction. Specifications are first expressed using the formalisms of linear temporal logic, signal temporal logic, and arithmetic constraints on Boolean variables. To reason about different requirements, we use specialized analysis and synthesis frameworks and formulate assume guarantee contracts at the articulation points in the design flow. We show the effectiveness of our approach on a proof-of-concept electric power system design.

Refactoring Real-time Specifications

This paper presents an approach to refactoring real-time specifications written using Real-Time Object-Z. This allows implementation components such as clocks and sensors, not necessarily present in an initial abstract specification, to be introduced via a sequence of refinement steps. The approach, based on similar work for Object-Z, is enabled by a semantics of object instantiation and operation synchronisation introduced in this paper. Means of refining synchronising operations to reflect the timing and causality constraints of an implementation are also presented.

Compositional specification and verification of distributed systems

We present a method for specification and verification of distributed systems that communicate via asynchronous message passing. The method handles both safety and liveness properties. It is compositional, i.e., a specification of a composite system can be obtained from specifications of its components. Specifications are given as labeled transition systems with fairness properties, using a program-like notation with guarded multiple assignments. Compositionality is attained by partitioning the labels of a transition system into input events, which intuitively denote message receptions, and output events, which intuitively denote message transmissions. A specification denotes a set of allowed sequences of message transmissions and receptions, in analogy with the way finite automata are used as acceptors of finite strings. A lower-level specification implements a higher-level one. We present a verification technique which reduces the problem of verifying the correctness of an implementation to classical verification conditions. Safety properties are verified by establishing a simulation relation between transition systems. Liveness properties are verified using methods for proving termination under fairness assumptions. Since specifications can be given at various levels of abstraction, the method is suitable in a development process where a detailed implementation is developed from an abstract specification through a sequence of refinement steps. As an application of the method, an algorithm by Thomas for updating a distributed database is specified and verified.