Michał Knapik

Bounded Parametric Verification for Distributed Time Petri Nets with Discrete-Time Semantics

Bounded Model Checking (BMC) is an efficient technique applicable to verification of temporal properties of (timed) distributed systems. In this paper we show for the first time how to apply BMC to parametric verification of time Petri nets with discrete-time semantics. The properties are expressed by formulas of the logic PRTECTL - a parametric extension of the existential fragment of Computation Tree Logic (CTL).

Parametric model checking with verICS

The paper presents the verification system VerICS, extended with the three new modules aimed at parametric verification of Elementary Net Systems, Distributed Time Petri Nets, and a subset of UML. All the modules exploit Bounded Model Checking for verifying parametric reachability and the properties specified in the logic PRTECTL - the parametric extension of the existential fragment of CTL.

Parameter Synthesis for Timed Kripke Structures

We show how to synthesise parameter values under which a given property, expressed in a certain extension of CTL, called RTCTLP, holds in a parametric timed Kripke structure. We prove the decidability of parameter synthesis for RTCTLP by showing how to restrict the infinite space of parameter valuations to its finite subset and employ a brute-force algorithm. The brute-force approach soon becomes intractable, therefore we propose a symbolic algorithm for RTCTLP parameter synthesis. Similarly to the fixed-point symbolic model checking approach, we introduce special operators which stabilise on the solution. The process of stabilisation is essentially a translation from the RTCTLP parameter synthesis problem to a discrete optimization task. We show that the proposed method is sound and complete and provide some complexity results. We argue that this approach leads to new opportunities in model checking, including the use of integer programming and related tools.

Action Synthesis for Branching Time Logic: Theory and Applications

We introduce a parametric extension of Action-Restricted Computation Tree Logic. A symbolic fixed-point algorithm providing a solution to the exhaustive parameter synthesis problem is proposed. The parametric approach allows for an in-depth system analysis and synthesis of correct parameter values. The time complexity of the problem and of the algorithm is provided. The prototype tool SPATULA, implementing the algorithm, is applied to the analysis of three benchmarks: faulty Train-Gate-Controller, Petersons Mutual Exclusion Protocol, and a Generic Pipeline Processing network. The experimental results show efficiency and scalability of our approach in comparison with a naive solution to the problem.

Controlling Actions and Time in Parametric Timed Automata

Cyber-physical systems involve both discrete actions and real-time that elapses depending on timing constants. In this paper, we introduce a formalism for such systems containing both real-time parameters in linear timing constraints and switchable (Boolean) actions. We define a new approach for synthesizing combinations of parameter valuations and allowed actions, under which the system correctness is ensured when expressed in the form of a safety property. We apply our approach to a railway crossing system example with a malicious intruder potentially threatening the system safety.

SMT-Based Parameter Synthesis for Parametric Timed Automata

We present a simple method for representing finite executions of Parametric Timed Automata using Satisfiability Modulo Theories (SMT). The transition relation of an automaton is translated to a formula of SMT, which is used to represent all the prefixes of a given length of all the executions. This enables to underapproximate the set of parameter valuations for the undecidable problem of parametric reachability. We introduce a freely available, open-source tool PTA2SMT and show its application to the synthesis of parameter valuations under which a timed mutual exclusion protocol fails.

Generating None-Plans in Order to Find Plans

We put forward a brand new approach to planning. The method aims at simplifying the task of planning in an abstract object-oriented domain where entities are added only and never removed. Our approach is based on the synthesis of a family of all sets of actions that cannot be composed into a plan (called none-plans) in order to prune the state space searched for plans. We show how to build a propositional formula describing a set of the none-plans and how to approximate this set when the task of planning becomes too complex. A preliminary evaluation of the application of the none-plans synthesis to the generation of plans in the PlanICS framework is shown. The experimental results show a high potential of the approach.

Fixed-Point Methods in Parametric Model Checking

We present a general framework for the synthesis of the constraints under which the selected properties hold in a class of models with discrete transitions, together with Boolean encoding - based method of implementing the theory. We introduce notions of parametric image and preimage, and show how to use them to build fixed-point algorithms for parametric model checking of reachability and deadlock freedom. An outline of how the ideas shown in this paper were specialized for an extension of Computation Tree Logic is given together with some experimental results.