SAFIR2010. The Finnish Research Programme on Safety 2007-2010. Final Report. Puska, Eija Karita &... more SAFIR2010. The Finnish Research Programme on Safety 2007-2010. Final Report. Puska, Eija Karita & Suolanen, Vesa. VTT Research Notes 2571, 55 - 65 The objective of the MODSAFE project was to evaluate and develop methods based on formal model checking and apply them in the safety analysis of NPP safety automation (I&C). The purpose was to develop and find a group of methods and tools that support utilities, regulators, vendors and support organizations in their practical safety evaluation efforts. The main tasks of the first two project years were to review the state of the art of employing formal methods and models for safety evaluation of industrial and nuclear safety systems, to develop basic methodology for applying model checking to safety evaluation, and to study the feasibility of the approach. The third and fourth project years concentrated on developing the approach more flexible and suitable for analysing larger and more complex models. The research was conducted by utilizi...
ABSTRACT Instrumentation and control (I&C) systems play a vital role in the operation of ... more ABSTRACT Instrumentation and control (I&C) systems play a vital role in the operation of safety-critical processes. Digital programmable logic controllers (PLC) enable sophisticated control tasks which sets high requirements for system validation and verification methods. Testing and simulation have an important role in the overall verification of a system but are not suitable for comprehensive evaluation because only a limited number of system behaviors can be analyzed due to time limitations. Testing is also performed too late in the development lifecycle and thus the correction of design errors is expensive. This paper discusses the role of formal methods in software development in the area of nuclear engineering. It puts forward model checking, a computer-aided formal method for verifying the correctness of a system design model, as a promising approach to system verification. The main contribution of the paper is the development of systematic methodology for modeling safety critical systems in the nuclear domain. Two case studies are reviewed, in which we have found errors that were previously not detected. We also discuss the actions that should be taken in order to increase confidence in the model checking process.
ABSTRACT Digital instrumentation and control (I&C) systems are increasingly used in the n... more ABSTRACT Digital instrumentation and control (I&C) systems are increasingly used in the nuclear engineering domain. The exhaustive verification of these systems is challenging, and the usual verification methods such as testing and simulation are typically insufficient. Model checking is a formal method that is able to exhaustively analyse the behaviour of a model against a formally written specification. If the model checking tool detects a violation of the specification, it will give out a counter-example that demonstrates how the specification is violated in the system. Unfortunately, sometimes real life system designs are too big to be directly analysed by traditional model checking techniques. We have developed an iterative technique for model checking large modular systems. The technique uses abstraction based over-approximations of the model behaviour, combined with iterative refinement. The main contribution of the work is the concrete abstraction refinement technique based on the modular structure of the model, the dependency graph of the model, and a refinement sampling heuristic similar to delta debugging. The technique is geared towards proving properties, and outperforms BDD-based model checking, the k-induction technique, and the property directed reachability algorithm (PDR) in our experiments.
Fifth International Conference on Application of Concurrency to System Design (ACSD'05), 2005
We consider the distributed implementability problem: Given a labeled transition system TS togeth... more We consider the distributed implementability problem: Given a labeled transition system TS together with a distribution ∆ of its actions over a set of processes, does there exist a distributed system over ∆ such that its global transition system is 'equivalent' to TS ? We work with the distributed system models of synchronous products of transition systems [1] and asynchronous automata . In this paper we provide complexity bounds for the above problem with three interpretations of 'equivalent': as transition system isomorphism, as language equivalence, and as bisimilarity. In particular, we solve problems left open in .
2013 13th International Conference on Application of Concurrency to System Design, 2013
We present an LTS-based (Labelled Transition System) CSP-like (Communicating Sequential Processes... more We present an LTS-based (Labelled Transition System) CSP-like (Communicating Sequential Processes) formalism for expressing parametrised systems. The parameters are process types, which determine the number of replicated components, and data types, which enable components with a parametrised state space. We prove that the formalism is compositional and show how to combine two existing results for parametrised verification in order to check trace refinement between parametrised processes. The combined approach gives upper bounds, i.e., cut-offs, for types such that a parametrised verification task collapses into finitely many checks solvable by using existing finite state refinement checking tools. We have implemented the approach and applied it to prove mutual exclusion properties of network protocols and systems with shared resources. To the best our knowledge, our technique is the only one that combines compositionality and completeness with support for multiple parametric process and data types.
Model checking is a very popular technique for the automatic verification of systems, widely appl... more Model checking is a very popular technique for the automatic verification of systems, widely applied by the hardware industry and already receiving considerable attention from software companies. It is based on the (possibly exhaustive) exploration of the states reached by the system along all its executions.
A new unfolding approach to LTL model checking is presented, in which the model checking problem ... more A new unfolding approach to LTL model checking is presented, in which the model checking problem can be solved by direct inspection of a certain finite prefix. The techniques presented so far required to run an elaborate algorithm on the prefix.
Instrumentation and control (I&C) systems play a crucial role in the operation of nuclear power p... more Instrumentation and control (I&C) systems play a crucial role in the operation of nuclear power plants (NPP) and other safety critical processes. An important change is the replacement of the old analogue I&C systems with new digitalised ones. The programmable digital logic controllers enable more complicated control tasks than the old analogue systems and thus the validation of the control
SAFIR2010. The Finnish Research Programme on Safety 2007-2010. Final Report. Puska, Eija Karita &... more SAFIR2010. The Finnish Research Programme on Safety 2007-2010. Final Report. Puska, Eija Karita & Suolanen, Vesa. VTT Research Notes 2571, 55 - 65 The objective of the MODSAFE project was to evaluate and develop methods based on formal model checking and apply them in the safety analysis of NPP safety automation (I&C). The purpose was to develop and find a group of methods and tools that support utilities, regulators, vendors and support organizations in their practical safety evaluation efforts. The main tasks of the first two project years were to review the state of the art of employing formal methods and models for safety evaluation of industrial and nuclear safety systems, to develop basic methodology for applying model checking to safety evaluation, and to study the feasibility of the approach. The third and fourth project years concentrated on developing the approach more flexible and suitable for analysing larger and more complex models. The research was conducted by utilizi...
ABSTRACT Instrumentation and control (I&C) systems play a vital role in the operation of ... more ABSTRACT Instrumentation and control (I&C) systems play a vital role in the operation of safety-critical processes. Digital programmable logic controllers (PLC) enable sophisticated control tasks which sets high requirements for system validation and verification methods. Testing and simulation have an important role in the overall verification of a system but are not suitable for comprehensive evaluation because only a limited number of system behaviors can be analyzed due to time limitations. Testing is also performed too late in the development lifecycle and thus the correction of design errors is expensive. This paper discusses the role of formal methods in software development in the area of nuclear engineering. It puts forward model checking, a computer-aided formal method for verifying the correctness of a system design model, as a promising approach to system verification. The main contribution of the paper is the development of systematic methodology for modeling safety critical systems in the nuclear domain. Two case studies are reviewed, in which we have found errors that were previously not detected. We also discuss the actions that should be taken in order to increase confidence in the model checking process.
ABSTRACT Digital instrumentation and control (I&C) systems are increasingly used in the n... more ABSTRACT Digital instrumentation and control (I&C) systems are increasingly used in the nuclear engineering domain. The exhaustive verification of these systems is challenging, and the usual verification methods such as testing and simulation are typically insufficient. Model checking is a formal method that is able to exhaustively analyse the behaviour of a model against a formally written specification. If the model checking tool detects a violation of the specification, it will give out a counter-example that demonstrates how the specification is violated in the system. Unfortunately, sometimes real life system designs are too big to be directly analysed by traditional model checking techniques. We have developed an iterative technique for model checking large modular systems. The technique uses abstraction based over-approximations of the model behaviour, combined with iterative refinement. The main contribution of the work is the concrete abstraction refinement technique based on the modular structure of the model, the dependency graph of the model, and a refinement sampling heuristic similar to delta debugging. The technique is geared towards proving properties, and outperforms BDD-based model checking, the k-induction technique, and the property directed reachability algorithm (PDR) in our experiments.
Fifth International Conference on Application of Concurrency to System Design (ACSD'05), 2005
We consider the distributed implementability problem: Given a labeled transition system TS togeth... more We consider the distributed implementability problem: Given a labeled transition system TS together with a distribution ∆ of its actions over a set of processes, does there exist a distributed system over ∆ such that its global transition system is 'equivalent' to TS ? We work with the distributed system models of synchronous products of transition systems [1] and asynchronous automata . In this paper we provide complexity bounds for the above problem with three interpretations of 'equivalent': as transition system isomorphism, as language equivalence, and as bisimilarity. In particular, we solve problems left open in .
2013 13th International Conference on Application of Concurrency to System Design, 2013
We present an LTS-based (Labelled Transition System) CSP-like (Communicating Sequential Processes... more We present an LTS-based (Labelled Transition System) CSP-like (Communicating Sequential Processes) formalism for expressing parametrised systems. The parameters are process types, which determine the number of replicated components, and data types, which enable components with a parametrised state space. We prove that the formalism is compositional and show how to combine two existing results for parametrised verification in order to check trace refinement between parametrised processes. The combined approach gives upper bounds, i.e., cut-offs, for types such that a parametrised verification task collapses into finitely many checks solvable by using existing finite state refinement checking tools. We have implemented the approach and applied it to prove mutual exclusion properties of network protocols and systems with shared resources. To the best our knowledge, our technique is the only one that combines compositionality and completeness with support for multiple parametric process and data types.
Model checking is a very popular technique for the automatic verification of systems, widely appl... more Model checking is a very popular technique for the automatic verification of systems, widely applied by the hardware industry and already receiving considerable attention from software companies. It is based on the (possibly exhaustive) exploration of the states reached by the system along all its executions.
A new unfolding approach to LTL model checking is presented, in which the model checking problem ... more A new unfolding approach to LTL model checking is presented, in which the model checking problem can be solved by direct inspection of a certain finite prefix. The techniques presented so far required to run an elaborate algorithm on the prefix.
Instrumentation and control (I&C) systems play a crucial role in the operation of nuclear power p... more Instrumentation and control (I&C) systems play a crucial role in the operation of nuclear power plants (NPP) and other safety critical processes. An important change is the replacement of the old analogue I&C systems with new digitalised ones. The programmable digital logic controllers enable more complicated control tasks than the old analogue systems and thus the validation of the control
This chapter presents the main technologies currently used in cloud computing, what are the main ... more This chapter presents the main technologies currently used in cloud computing, what are the main commercial offerings and what are their programming models. We discuss hardware virtualization technologies used in datacenters, three different service abstraction levels: infrastructure, platform and application and the main driver and adoption problems in cloud computing.
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Papers by Keijo Heljanko