Fully Symbolic TCTL Model Checking for Incomplete Timed Systems

In this paper we present a fully symbolic TCTL model checking algorithm for incomplete timed systems. Our algorithm is able to prove that a TCTL property is violated or satisfied regardless of the implementation of unknown timed components in the system. For that purpose the algorithm computes over- approximations of sets of states fulfilling a TCTL property φ for at least one implementation of the unknown components and under-approximations of sets of states fulfilling φ for all possible implementations of the unknown components. The algorithm works on a symbolic model for timed systems, called a finite state machine with time (FSMT), and makes use of fully symbolic state set representations containing both the clock values and the state variables. In order to handle incomplete timed systems our model checking algorithm deals with different communication methods between the system and its unknown components, e.g. shared integer variables and urgent and non-urgent synchronization. Our experimental results demonstrate that it is possible to prove interesting properties at early stages of the design when parts of the overall system may not yet be finished. Additionally, fading out components of a large system may dramatically reduce the complexity of the system and thus the effort for verification

Compositional Verification for Timed Systems Based on Automatic Invariant Generation

We propose a method for compositional verification to address the state space explosion problem inherent to model-checking timed systems with a large number of components. The main challenge is to obtain pertinent global timing constraints from the timings in the components alone. To this end, we make use of auxiliary clocks to automatically generate new invariants which capture the constraints induced by the synchronisations between components. The method has been implemented in the RTD-Finder tool and successfully experimented on several benchmarks

Verifying collision avoidance behaviours for unmanned surface vehicles using probabilistic model checking

Collision avoidance is an essential safety requirement for unmanned surface vehicles (USVs). Normally, its practical verification is non-trivial, due to the stochastic behaviours of both the USVs and the intruders. This paper presents the probabilistic timed automata (PTAs) based formalism for three collision avoidance behaviours of USVs in uncertain dynamic environments, which are associated with the crossing situation in COLREGs. Steering right, acceleration, and deceleration are considered potential evasive manoeuvres. The state-of-the-art prism model checker is applied to analyse the underlying models. This work provides a framework and practical application of the probabilistic model checking for decision making in collision avoidance for USVs

Learning to Prove Safety over Parameterised Concurrent Systems (Full Version)

We revisit the classic problem of proving safety over parameterised concurrent systems, i.e., an infinite family of finite-state concurrent systems that are represented by some finite (symbolic) means. An example of such an infinite family is a dining philosopher protocol with any number n of processes (n being the parameter that defines the infinite family). Regular model checking is a well-known generic framework for modelling parameterised concurrent systems, where an infinite set of configurations (resp. transitions) is represented by a regular set (resp. regular transducer). Although verifying safety properties in the regular model checking framework is undecidable in general, many sophisticated semi-algorithms have been developed in the past fifteen years that can successfully prove safety in many practical instances. In this paper, we propose a simple solution to synthesise regular inductive invariants that makes use of Angluin's classic L* algorithm (and its variants). We provide a termination guarantee when the set of configurations reachable from a given set of initial configurations is regular. We have tested L* algorithm on standard (as well as new) examples in regular model checking including the dining philosopher protocol, the dining cryptographer protocol, and several mutual exclusion protocols (e.g. Bakery, Burns, Szymanski, and German). Our experiments show that, despite the simplicity of our solution, it can perform at least as well as existing semi-algorithms.Comment: Full version of FMCAD'17 pape

Using formal methods to support testing

Formal methods and testing are two important approaches that assist in the development of high quality software. While traditionally these approaches have been seen as rivals, in recent years a new consensus has developed in which they are seen as complementary. This article reviews the state of the art regarding ways in which the presence of a formal specification can be used to assist testing

Modeling and verifying the FlexRay physical layer protocol with reachability checking of timed automata

In this thesis, I report on the verification of the resilience of the FlexRay automotive bus protocol's physical layer protocol against glitches during message transmission and drifting clocks. This entailed modeling a significant part of this industrially used communictation protocol and the underlying hardware as well as the possible error scenarios in fine detail. Verifying such a complex model with model-checking led me to the development of data-structures and algorithms able to handle the associated complexity using only reasonable resources. This thesis presents such data-structures and algorithms for reachability checking of timed automata. It also present modeling principles enabling the construction of timed automata models that can be efficiently checked, as well as the models arrived at. Finally, it reports on the verified resilience of FlexRay's physical layer protocol against specific patterns of glitches under varying assumptions about the underlying hardware, like clock drift.In dieser Dissertation berichte ich über den Nachweis der Resilienz des Bitübertragungsprotokolls für die physikalische Schicht des FlexRay-Fahrzeugbusprotokolls gegenüber Übertragungsfehlern und Uhrenverschiebung. Dafür wurde es notwendig, einen signifikanten Teil dieses industriell genutzten Kommunikationsprotokolls mit seiner Hardwareumgebung und die möglichen Fehlerszenarien detailliert zu modellieren. Ein so komplexes Modell mittels Modellprüfung zu überprüfen führte mich zur Entwicklung von Datenstrukturen und Algorithmen, die die damit verbundene Komplexität mit vernünftigen Ressourcenanforderungen bewältigen können. Diese Dissertation stellt solche Datenstrukturen und Algorithmen zur Erreichbarkeitsprüfung gezeiteter Automaten vor. Sie stellt auch Modellierungsprinzipien vor, die es ermöglichen, Modelle in Form gezeiteter Automaten zu konstruieren, die effizient überprüft werden können, sowie die erstellten Modelle. Schließlich berichtet sie über die überprüfte Resilienz des FlexRay-Bitübertragungsprotokolls gegenüber spezifischen Übertragungsfehlermustern unter verschiedenen Annahmen über die Hardwareumgebung, wie etwa die Uhrenverschiebung.DFG: SFB/TRR 14 "AVACS - Automatische Verifikation und Analyse komplexer Systeme

Setting Parameters for Biological Models With ANIMO

ANIMO (Analysis of Networks with Interactive MOdeling) is a software for modeling biological networks, such as e.g. signaling, metabolic or gene networks. An ANIMO model is essentially the sum of a network topology and a number of interaction parameters. The topology describes the interactions between biological entities in form of a graph, while the parameters determine the speed of occurrence of such interactions. When a mismatch is observed between the behavior of an ANIMO model and experimental data, we want to update the model so that it explains the new data. In general, the topology of a model can be expanded with new (known or hypothetical) nodes, and enables it to match experimental data. However, the unrestrained addition of new parts to a model causes two problems: models can become too complex too fast, to the point of being intractable, and too many parts marked as "hypothetical" or "not known" make a model unrealistic. Even if changing the topology is normally the easier task, these problems push us to try a better parameter fit as a first step, and resort to modifying the model topology only as a last resource. In this paper we show the support added in ANIMO to ease the task of expanding the knowledge on biological networks, concentrating in particular on the parameter settings