Recent work on Alternating-Time Temporal Logic and Coalition Logic has allowed the expression of many interesting properties of coalitions and strategies. However there is no natural way of expressing resource requirements in these logics. This paper presents a Resource-Bounded Coalition Logic (RBCL) which has explicit representation of resource bounds in the language, and gives a complete and sound axiomatisation of RBCL.
Several logics for expressing coalitional ability under resource bounds have been proposed and studied in the literature. Previous work has shown that if only consumption of resources is considered or the total amount of resources produced or consumed on any path in the system is bounded, then the model-checking problem for several standard logics, such as Resource-Bounded Coalition Logic (RB-CL) and Resource-Bounded Alternating-Time Temporal Logic (RB-ATL) is decidable. However, for coalition logics with unbounded resource production and consumption, only some undecidability results are known. In this paper, we show that the model-checking problem for RB-ATL with unbounded production and consumption of resources is decidable but EXPSPACE-hard. We also investigate some tractable cases and provide a detailed comparison to a variant of the resource logic RAL, together with new complexity results.
Abstract. The safety analysis of interlocking railway systems involves verifying collision and derailment freedom. In this paper we propose a structured way of refining track plans, in order to expand track segments so that they form collections of track segments. We show how the abstract model can be model checked to ensure the safety properties, which must also hold in the corresponding concrete track plan, so that we will never need to model check the concrete track plan directly. We also identify the minimal number of trains that needs to be considered as part of the model checking, and we demonstrate the practicality of the approach on various scenarios.
Abstract. We describe a novel framework for modelling railway interlockings which has been developed in conjunction with railway engineers. The modelling language used is CSP||B. Beyond the modelling we present a variety of abstraction techniques which make the analysis of medium to large scale networks feasible. The paper notably introduces a covering technique that allows railway scheme plans to be decomposed into a set of smaller scheme plans. The finitisation and topological abstraction techniques are extended from previous work and are given formal foundations. All three techniques are applicable to other modelling frameworks besides CSP||B. Being able to apply abstractions and simplifications on the domain model before performing model checking is the key strength of our approach. We demonstrate the use of the framework on a real-life, medium size scheme plan.
The safety analysis of interlocking railway systems involves verifying freedom from collision, derailment and run-through (that is, trains rolling over wrongly-set points). Typically, various unrealistic assumptions are made in order to facilitate their analyses. In particular, trains are invariably assumed to be shorter than track segments; and generally only a very few trains are allowed to be introduced into the network under consideration.In this paper we propose modelling methodologies which elegantly dismiss these assumptions. We first provide a framework for modelling arbitrarily many trains of arbitrary length in a network; and then we demonstrate that it is enough with our modelling approach to consider only two trains when verifying safety conditions. That is, if a safety violation appears in the original model with any number of trains of any and varying lengths, then a violation will be exposed in the simpler model with only two trains. Importantly, our modelling framework has been developed alongside -and in conjunction with -railway engineers. It is vital that they can validate the models and verification conditions, and -in the case of design errors -obtain comprehensible feedback. We demonstrate our modelling and abstraction techniques on two simple interlocking systems proposed by our industrial partner. As our formalization is, by design, near to their way of thinking, they are comfortable with it and trust it.
Abstract. The paper presents a tool-supported approach to graphically editing scheme plans and their safety verification. The graphical tool is based on a Domain Specific Language which is used as the basis for transformation to a CSP B formal model of a scheme plan. The models produced utilise a variety of abstraction techniques that make the analysis of large scale plans feasible. The techniques are applicable to other modelling languages besides CSP B. We use the ProB tool to ensure the safety properties of collision, derailment and run-through freedom.
Abstract. Railways need to be safe and, at the same time, should offer high capacity. While the notion of safety is well understood in the railway domain, the meaning of capacity is understood only on an intuitive and informal level. In this study, we show how to define and analyse capacity in a rigorous way. Our modelling approach builds on an established modelling technique in the process algebra Csp for safety alone, provides an integrated view on safety as well as capacity, and offers proof support in terms of (untimed) model checking.
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