TY - CONF
AB - We present the results of a friendly competition for formal verification of continuous and hybrid systems with nonlinear continuous dynamics. The friendly competition took place as part of the workshop Applied Verification for Continuous and Hybrid Systems (ARCH) in 2019. In this year, 6 tools Ariadne, CORA, DynIbex, Flow*, Isabelle/HOL, and JuliaReach (in alphabetic order) participated. They are applied to solve reachability analysis problems on four benchmark problems, one of them with hybrid dynamics. We do not rank the tools based on the results, but show the current status and discover the potential advantages of different tools.
AU - Immler, Fabian
AU - Althoff, Matthias
AU - Benet, Luis
AU - Chapoutot, Alexandre
AU - Chen, Xin
AU - Forets, Marcelo
AU - Geretti, Luca
AU - Kochdumper, Niklas
AU - Sanders, David P.
AU - Schilling, Christian
ID - 7576
T2 - EPiC Series in Computing
TI - ARCH-COMP19 Category Report: Continuous and hybrid systems with nonlinear dynamics
VL - 61
ER -
TY - JOUR
AB - Two-player games on graphs are widely studied in formal methods, as they model the interaction between a system and its environment. The game is played by moving a token throughout a graph to produce an infinite path. There are several common modes to determine how the players move the token through the graph; e.g., in turn-based games the players alternate turns in moving the token. We study the bidding mode of moving the token, which, to the best of our knowledge, has never been studied in infinite-duration games. The following bidding rule was previously defined and called Richman bidding. Both players have separate budgets, which sum up to 1. In each turn, a bidding takes place: Both players submit bids simultaneously, where a bid is legal if it does not exceed the available budget, and the higher bidder pays his bid to the other player and moves the token. The central question studied in bidding games is a necessary and sufficient initial budget for winning the game: a threshold budget in a vertex is a value t ∈ [0, 1] such that if Player 1’s budget exceeds t, he can win the game; and if Player 2’s budget exceeds 1 − t, he can win the game. Threshold budgets were previously shown to exist in every vertex of a reachability game, which have an interesting connection with random-turn games—a sub-class of simple stochastic games in which the player who moves is chosen randomly. We show the existence of threshold budgets for a qualitative class of infinite-duration games, namely parity games, and a quantitative class, namely mean-payoff games. The key component of the proof is a quantitative solution to strongly connected mean-payoff bidding games in which we extend the connection with random-turn games to these games, and construct explicit optimal strategies for both players.
AU - Avni, Guy
AU - Henzinger, Thomas A
AU - Chonev, Ventsislav K
ID - 6752
IS - 4
JF - Journal of the ACM
SN - 00045411
TI - Infinite-duration bidding games
VL - 66
ER -
TY - CONF
AB - We address the problem of analyzing the reachable set of a polynomial nonlinear continuous system by over-approximating the flowpipe of its dynamics. The common approach to tackle this problem is to perform a numerical integration over a given time horizon based on Taylor expansion and interval arithmetic. However, this method results to be very conservative when there is a large difference in speed between trajectories as time progresses. In this paper, we propose to use combinations of barrier functions, which we call piecewise barrier tube (PBT), to over-approximate flowpipe. The basic idea of PBT is that for each segment of a flowpipe, a coarse box which is big enough to contain the segment is constructed using sampled simulation and then in the box we compute by linear programming a set of barrier functions (called barrier tube or BT for short) which work together to form a tube surrounding the flowpipe. The benefit of using PBT is that (1) BT is independent of time and hence can avoid being stretched and deformed by time; and (2) a small number of BTs can form a tight over-approximation for the flowpipe, which means that the computation required to decide whether the BTs intersect the unsafe set can be reduced significantly. We implemented a prototype called PBTS in C++. Experiments on some benchmark systems show that our approach is effective.
AU - Kong, Hui
AU - Bartocci, Ezio
AU - Henzinger, Thomas A
ID - 142
TI - Reachable set over-approximation for nonlinear systems using piecewise barrier tubes
VL - 10981
ER -
TY - CONF
AB - The task of a monitor is to watch, at run-time, the execution of a reactive system, and signal the occurrence of a safety violation in the observed sequence of events. While finite-state monitors have been studied extensively, in practice, monitoring software also makes use of unbounded memory. We define a model of automata equipped with integer-valued registers which can execute only a bounded number of instructions between consecutive events, and thus can form the theoretical basis for the study of infinite-state monitors. We classify these register monitors according to the number k of available registers, and the type of register instructions. In stark contrast to the theory of computability for register machines, we prove that for every k 1, monitors with k + 1 counters (with instruction set 〈+1, =〉) are strictly more expressive than monitors with k counters. We also show that adder monitors (with instruction set 〈1, +, =〉) are strictly more expressive than counter monitors, but are complete for monitoring all computable safety -languages for k = 6. Real-time monitors are further required to signal the occurrence of a safety violation as soon as it occurs. The expressiveness hierarchy for counter monitors carries over to real-time monitors. We then show that 2 adders cannot simulate 3 counters in real-time. Finally, we show that real-time adder monitors with inequalities are as expressive as real-time Turing machines.
AU - Ferrere, Thomas
AU - Henzinger, Thomas A
AU - Saraç, Ege
ID - 144
TI - A theory of register monitors
VL - Part F138033
ER -
TY - CONF
AB - Imprecision in timing can sometimes be beneficial: Metric interval temporal logic (MITL), disabling the expression of punctuality constraints, was shown to translate to timed automata, yielding an elementary decision procedure. We show how this principle extends to other forms of dense-time specification using regular expressions. By providing a clean, automaton-based formal framework for non-punctual languages, we are able to recover and extend several results in timed systems. Metric interval regular expressions (MIRE) are introduced, providing regular expressions with non-singular duration constraints. We obtain that MIRE are expressively complete relative to a class of one-clock timed automata, which can be determinized using additional clocks. Metric interval dynamic logic (MIDL) is then defined using MIRE as temporal modalities. We show that MIDL generalizes known extensions of MITL, while translating to timed automata at comparable cost.
AU - Ferrere, Thomas
ID - 156
TI - The compound interest in relaxing punctuality
VL - 10951
ER -
TY - CONF
AB - We describe a new algorithm for the parametric identification problem for signal temporal logic (STL), stated as follows. Given a densetime real-valued signal w and a parameterized temporal logic formula φ, compute the subset of the parameter space that renders the formula satisfied by the signal. Unlike previous solutions, which were based on search in the parameter space or quantifier elimination, our procedure works recursively on φ and computes the evolution over time of the set of valid parameter assignments. This procedure is similar to that of monitoring or computing the robustness of φ relative to w. Our implementation and experiments demonstrate that this approach can work well in practice.
AU - Bakhirkin, Alexey
AU - Ferrere, Thomas
AU - Maler, Oded
ID - 182
SN - 978-1-4503-5642-8
T2 - Proceedings of the 21st International Conference on Hybrid Systems
TI - Efficient parametric identification for STL
ER -
TY - CONF
AB - Fault-localization is considered to be a very tedious and time-consuming activity in the design of complex Cyber-Physical Systems (CPS). This laborious task essentially requires expert knowledge of the system in order to discover the cause of the fault. In this context, we propose a new procedure that AIDS designers in debugging Simulink/Stateflow hybrid system models, guided by Signal Temporal Logic (STL) specifications. The proposed method relies on three main ingredients: (1) a monitoring and a trace diagnostics procedure that checks whether a tested behavior satisfies or violates an STL specification, localizes time segments and interfaces variables contributing to the property violations; (2) a slicing procedure that maps these observable behavior segments to the internal states and transitions of the Simulink model; and (3) a spectrum-based fault-localization method that combines the previous analysis from multiple tests to identify the internal states and/or transitions that are the most likely to explain the fault. We demonstrate the applicability of our approach on two Simulink models from the automotive and the avionics domain.
AU - Bartocci, Ezio
AU - Ferrere, Thomas
AU - Manjunath, Niveditha
AU - Nickovic, Dejan
ID - 183
TI - Localizing faults in simulink/stateflow models with STL
ER -
TY - CONF
AB - Partially-observable Markov decision processes (POMDPs) with discounted-sum payoff are a standard framework to model a wide range of problems related to decision making under uncertainty. Traditionally, the goal has been to obtain policies that optimize the expectation of the discounted-sum payoff. A key drawback of the expectation measure is that even low probability events with extreme payoff can significantly affect the expectation, and thus the obtained policies are not necessarily risk-averse. An alternate approach is to optimize the probability that the payoff is above a certain threshold, which allows obtaining risk-averse policies, but ignores optimization of the expectation. We consider the expectation optimization with probabilistic guarantee (EOPG) problem, where the goal is to optimize the expectation ensuring that the payoff is above a given threshold with at least a specified probability. We present several results on the EOPG problem, including the first algorithm to solve it.
AU - Chatterjee, Krishnendu
AU - Elgyütt, Adrian
AU - Novotny, Petr
AU - Rouillé, Owen
ID - 24
TI - Expectation optimization with probabilistic guarantees in POMDPs with discounted-sum objectives
VL - 2018
ER -
TY - CONF
AB - We introduce in this paper AMT 2.0 , a tool for qualitative and quantitative analysis of hybrid continuous and Boolean signals that combine numerical values and discrete events. The evaluation of the signals is based on rich temporal specifications expressed in extended Signal Temporal Logic (xSTL), which integrates Timed Regular Expressions (TRE) within Signal Temporal Logic (STL). The tool features qualitative monitoring (property satisfaction checking), trace diagnostics for explaining and justifying property violations and specification-driven measurement of quantitative features of the signal.
AU - Nickovic, Dejan
AU - Lebeltel, Olivier
AU - Maler, Oded
AU - Ferrere, Thomas
AU - Ulus, Dogan
ED - Beyer, Dirk
ED - Huisman, Marieke
ID - 299
TI - AMT 2.0: Qualitative and quantitative trace analysis with extended signal temporal logic
VL - 10806
ER -
TY - CONF
AB - Graph games played by two players over finite-state graphs are central in many problems in computer science. In particular, graph games with ω -regular winning conditions, specified as parity objectives, which can express properties such as safety, liveness, fairness, are the basic framework for verification and synthesis of reactive systems. The decisions for a player at various states of the graph game are represented as strategies. While the algorithmic problem for solving graph games with parity objectives has been widely studied, the most prominent data-structure for strategy representation in graph games has been binary decision diagrams (BDDs). However, due to the bit-level representation, BDDs do not retain the inherent flavor of the decisions of strategies, and are notoriously hard to minimize to obtain succinct representation. In this work we propose decision trees for strategy representation in graph games. Decision trees retain the flavor of decisions of strategies and allow entropy-based minimization to obtain succinct trees. However, decision trees work in settings (e.g., probabilistic models) where errors are allowed, and overfitting of data is typically avoided. In contrast, for strategies in graph games no error is allowed, and the decision tree must represent the entire strategy. We develop new techniques to extend decision trees to overcome the above obstacles, while retaining the entropy-based techniques to obtain succinct trees. We have implemented our techniques to extend the existing decision tree solvers. We present experimental results for problems in reactive synthesis to show that decision trees provide a much more efficient data-structure for strategy representation as compared to BDDs.
AU - Brázdil, Tomáš
AU - Chatterjee, Krishnendu
AU - Kretinsky, Jan
AU - Toman, Viktor
ID - 297
TI - Strategy representation by decision trees in reactive synthesis
VL - 10805
ER -
TY - BOOK
AB - This book first explores the origins of this idea, grounded in theoretical work on temporal logic and automata. The editors and authors are among the world's leading researchers in this domain, and they contributed 32 chapters representing a thorough view of the development and application of the technique. Topics covered include binary decision diagrams, symbolic model checking, satisfiability modulo theories, partial-order reduction, abstraction, interpolation, concurrency, security protocols, games, probabilistic model checking, and process algebra, and chapters on the transfer of theory to industrial practice, property specification languages for hardware, and verification of real-time systems and hybrid systems.
The book will be valuable for researchers and graduate students engaged with the development of formal methods and verification tools.
AU - Clarke, Edmund M.
AU - Henzinger, Thomas A
AU - Veith, Helmut
AU - Bloem, Roderick
ID - 3300
TI - Handbook of model checking
ER -
TY - JOUR
AB - In this paper, we present a formal model-driven design approach to establish a safety-assured implementation of multifunction vehicle bus controller (MVBC), which controls the data transmission among the devices of the vehicle. First, the generic models and safety requirements described in International Electrotechnical Commission Standard 61375 are formalized as time automata and timed computation tree logic formulas, respectively. With model checking tool Uppaal, we verify whether or not the constructed timed automata satisfy the formulas and several logic inconsistencies in the original standard are detected and corrected. Then, we apply the code generation tool Times to generate C code from the verified model, which is later synthesized into a real MVBC chip, with some handwriting glue code. Furthermore, the runtime verification tool RMOR is applied on the integrated code, to verify some safety requirements that cannot be formalized on the timed automata. For evaluation, we compare the proposed approach with existing MVBC design methods, such as BeagleBone, Galsblock, and Simulink. Experiments show that more ambiguousness or bugs in the standard are detected during Uppaal verification, and the generated code of Times outperforms the C code generated by others in terms of the synthesized binary code size. The errors in the standard have been confirmed and the resulting MVBC has been deployed in the real train communication network.
AU - Jiang, Yu
AU - Liu, Han
AU - Song, Huobing
AU - Kong, Hui
AU - Wang, Rui
AU - Guan, Yong
AU - Sha, Lui
ID - 434
IS - 10
JF - IEEE Transactions on Intelligent Transportation Systems
TI - Safety-assured model-driven design of the multifunction vehicle bus controller
VL - 19
ER -
TY - JOUR
AB - Recently, contract-based design has been proposed as an “orthogonal” approach that complements system design methodologies proposed so far to cope with the complexity of system design. Contract-based design provides a rigorous scaffolding for verification, analysis, abstraction/refinement, and even synthesis. A number of results have been obtained in this domain but a unified treatment of the topic that can help put contract-based design in perspective was missing. This monograph intends to provide such a treatment where contracts are precisely defined and characterized so that they can be used in design methodologies with no ambiguity. In particular, this monograph identifies the essence of complex system design using contracts through a mathematical “meta-theory”, where all the properties of the methodology are derived from a very abstract and generic notion of contract. We show that the meta-theory provides deep and illuminating links with existing contract and interface theories, as well as guidelines for designing new theories. Our study encompasses contracts for both software and systems, with emphasis on the latter. We illustrate the use of contracts with two examples: requirement engineering for a parking garage management, and the development of contracts for timing and scheduling in the context of the Autosar methodology in use in the automotive sector.
AU - Benveniste, Albert
AU - Nickovic, Dejan
AU - Caillaud, Benoît
AU - Passerone, Roberto
AU - Raclet, Jean Baptiste
AU - Reinkemeier, Philipp
AU - Sangiovanni-Vincentelli, Alberto
AU - Damm, Werner
AU - Henzinger, Thomas A
AU - Larsen, Kim G.
ID - 5677
IS - 2-3
JF - Foundations and Trends in Electronic Design Automation
SN - 15513939
TI - Contracts for system design
VL - 12
ER -
TY - CONF
AB - In two-player games on graphs, the players move a token through a graph to produce an infinite path, which determines the winner or payoff of the game. Such games are central in formal verification since they model the interaction between a non-terminating system and its environment. We study bidding games in which the players bid for the right to move the token. Two bidding rules have been defined. In Richman bidding, in each round, the players simultaneously submit bids, and the higher bidder moves the token and pays the other player. Poorman bidding is similar except that the winner of the bidding pays the “bank” rather than the other player. While poorman reachability games have been studied before, we present, for the first time, results on infinite-duration poorman games. A central quantity in these games is the ratio between the two players’ initial budgets. The questions we study concern a necessary and sufficient ratio with which a player can achieve a goal. For reachability objectives, such threshold ratios are known to exist for both bidding rules. We show that the properties of poorman reachability games extend to complex qualitative objectives such as parity, similarly to the Richman case. Our most interesting results concern quantitative poorman games, namely poorman mean-payoff games, where we construct optimal strategies depending on the initial ratio, by showing a connection with random-turn based games. The connection in itself is interesting, because it does not hold for reachability poorman games. We also solve the complexity problems that arise in poorman bidding games.
AU - Avni, Guy
AU - Henzinger, Thomas A
AU - Ibsen-Jensen, Rasmus
ID - 5788
SN - 03029743
TI - Infinite-duration poorman-bidding games
VL - 11316
ER -
TY - CONF
AB - Formalizing properties of systems with continuous dynamics is a challenging task. In this paper, we propose a formal framework for specifying and monitoring rich temporal properties of real-valued signals. We introduce signal first-order logic (SFO) as a specification language that combines first-order logic with linear-real arithmetic and unary function symbols interpreted as piecewise-linear signals. We first show that while the satisfiability problem for SFO is undecidable, its membership and monitoring problems are decidable. We develop an offline monitoring procedure for SFO that has polynomial complexity in the size of the input trace and the specification, for a fixed number of quantifiers and function symbols. We show that the algorithm has computation time linear in the size of the input trace for the important fragment of bounded-response specifications interpreted over input traces with finite variability. We can use our results to extend signal temporal logic with first-order quantifiers over time and value parameters, while preserving its efficient monitoring. We finally demonstrate the practical appeal of our logic through a case study in the micro-electronics domain.
AU - Bakhirkin, Alexey
AU - Ferrere, Thomas
AU - Henzinger, Thomas A
AU - Nickovicl, Deian
ID - 5959
SN - 9781538655603
T2 - 2018 International Conference on Embedded Software
TI - Keynote: The first-order logic of signals
ER -
TY - CHAP
AB - Model checking is a computer-assisted method for the analysis of dynamical systems that can be modeled by state-transition systems. Drawing from research traditions in mathematical logic, programming languages, hardware design, and theoretical computer science, model checking is now widely used for the verification of hardware and software in industry. This chapter is an introduction and short survey of model checking. The chapter aims to motivate and link the individual chapters of the handbook, and to provide context for readers who are not familiar with model checking.
AU - Clarke, Edmund
AU - Henzinger, Thomas A
AU - Veith, Helmut
ED - Henzinger, Thomas A
ID - 60
T2 - Handbook of Model Checking
TI - Introduction to model checking
ER -
TY - JOUR
AB - Network games (NGs) are played on directed graphs and are extensively used in network design and analysis. Search problems for NGs include finding special strategy profiles such as a Nash equilibrium and a globally-optimal solution. The networks modeled by NGs may be huge. In formal verification, abstraction has proven to be an extremely effective technique for reasoning about systems with big and even infinite state spaces. We describe an abstraction-refinement methodology for reasoning about NGs. Our methodology is based on an abstraction function that maps the state space of an NG to a much smaller state space. We search for a global optimum and a Nash equilibrium by reasoning on an under- and an over-approximation defined on top of this smaller state space. When the approximations are too coarse to find such profiles, we refine the abstraction function. We extend the abstraction-refinement methodology to labeled networks, where the objectives of the players are regular languages. Our experimental results demonstrate the effectiveness of the methodology.
AU - Avni, Guy
AU - Guha, Shibashis
AU - Kupferman, Orna
ID - 6006
IS - 3
JF - Games
SN - 2073-4336
TI - An abstraction-refinement methodology for reasoning about network games
VL - 9
ER -
TY - JOUR
AB - Synthesis is the automated construction of a system from its specification. In real life, hardware and software systems are rarely constructed from scratch. Rather, a system is typically constructed from a library of components. Lustig and Vardi formalized this intuition and studied LTL synthesis from component libraries. In real life, designers seek optimal systems. In this paper we add optimality considerations to the setting. We distinguish between quality considerations (for example, size - the smaller a system is, the better it is), and pricing (for example, the payment to the company who manufactured the component). We study the problem of designing systems with minimal quality-cost and price. A key point is that while the quality cost is individual - the choices of a designer are independent of choices made by other designers that use the same library, pricing gives rise to a resource-allocation game - designers that use the same component share its price, with the share being proportional to the number of uses (a component can be used several times in a design). We study both closed and open settings, and in both we solve the problem of finding an optimal design. In a setting with multiple designers, we also study the game-theoretic problems of the induced resource-allocation game.
AU - Avni, Guy
AU - Kupferman, Orna
ID - 608
JF - Theoretical Computer Science
TI - Synthesis from component libraries with costs
VL - 712
ER -
TY - CONF
AB - Reachability analysis is difficult for hybrid automata with affine differential equations, because the reach set needs to be approximated. Promising abstraction techniques usually employ interval methods or template polyhedra. Interval methods account for dense time and guarantee soundness, and there are interval-based tools that overapproximate affine flowpipes. But interval methods impose bounded and rigid shapes, which make refinement expensive and fixpoint detection difficult. Template polyhedra, on the other hand, can be adapted flexibly and can be unbounded, but sound template refinement for unbounded reachability analysis has been implemented only for systems with piecewise constant dynamics. We capitalize on the advantages of both techniques, combining interval arithmetic and template polyhedra, using the former to abstract time and the latter to abstract space. During a CEGAR loop, whenever a spurious error trajectory is found, we compute additional space constraints and split time intervals, and use these space-time interpolants to eliminate the counterexample. Space-time interpolation offers a lazy, flexible framework for increasing precision while guaranteeing soundness, both for error avoidance and fixpoint detection. To the best of out knowledge, this is the first abstraction refinement scheme for the reachability analysis over unbounded and dense time of affine hybrid systems, which is both sound and automatic. We demonstrate the effectiveness of our algorithm with several benchmark examples, which cannot be handled by other tools.
AU - Frehse, Goran
AU - Giacobbe, Mirco
AU - Henzinger, Thomas A
ID - 140
SN - 03029743
TI - Space-time interpolants
VL - 10981
ER -
TY - CONF
AB - Network games are widely used as a model for selfish resource-allocation problems. In the classicalmodel, each player selects a path connecting her source and target vertices. The cost of traversingan edge depends on theload; namely, number of players that traverse it. Thus, it abstracts the factthat different users may use a resource at different times and for different durations, which playsan important role in determining the costs of the users in reality. For example, when transmittingpackets in a communication network, routing traffic in a road network, or processing a task in aproduction system, actual sharing and congestion of resources crucially depends on time.In [13], we introducedtimed network games, which add a time component to network games.Each vertexvin the network is associated with a cost function, mapping the load onvto theprice that a player pays for staying invfor one time unit with this load. Each edge in thenetwork is guarded by the time intervals in which it can be traversed, which forces the players tospend time in the vertices. In this work we significantly extend the way time can be referred toin timed network games. In the model we study, the network is equipped withclocks, and, as intimed automata, edges are guarded by constraints on the values of the clocks, and their traversalmay involve a reset of some clocks. We argue that the stronger model captures many realisticnetworks. The addition of clocks breaks the techniques we developed in [13] and we developnew techniques in order to show that positive results on classic network games carry over to thestronger timed setting.
AU - Avni, Guy
AU - Guha, Shibashis
AU - Kupferman, Orna
ID - 6005
TI - Timed network games with clocks
VL - 117
ER -