While waiting for the millennium: Formal specification and verification of concurrent systems now

This book is a celebration of Leslie Lamport's work on concurrency, interwoven in four-and-a-half decades of an evolving industry: from the introduction of the first personal computer to an era when parallel and distributed multiprocessors are abundant. His works lay formal foundations for concurrent computations executed by interconnected computers. Some of the algorithms have become standard engineering practice for fault tolerant distributed computing - distributed systems that continue to function correctly despite failures of individual components. He also developed a substantial body of work on the formal specification and verification of concurrent systems, and has contributed to the development of automated tools applying these methods. Part I consists of technical chapters of the book and a biography. The technical chapters of this book present a retrospective on Lamport's original ideas from experts in the field. Through this lens, it portrays their long-lasting impact. The chapters cover timeless notions Lamport introduced: the Bakery algorithm, atomic shared registers and sequential consistency; causality and logical time; Byzantine Agreement; state machine replication and Paxos; temporal logic of actions (TLA). The professional biography tells of Lamport's career, providing the context in which his work arose and broke new grounds, and discusses LaTeX - perhaps Lamport's most influential contribution outside the field of concurrency. This chapter gives a voice to the people behind the achievements, notably Lamport himself, and additionally the colleagues around him, who inspired, collaborated, and helped him drive worldwide impact. Part II consists of a selection of Leslie Lamport's most influential papers. This book touches on a lifetime of contributions by Leslie Lamport to the field of concurrency and on the extensive influence he had on people working in the field. It will be of value to historians of science, and to researchers and students who work in the area of concurrency and who are interested to read about the work of one of the most influential researchers in this field.

Performing formal verification of concurrent systems involves partial order logics (here MSO with partial orders) for the specification of properties or of the concurrent system itself. A common structure for the verification of concurrent systems is so-called pomset. A pomset is a multiset of partially ordered events. The partial order relation describes causal dependencies of events. We propose a new word based model, namely Pre-Post-Pomset, making the exploration of pomsets space possible. In this paper, our new model stands to be a general model in the sense that some classical models used in the specification of concurrent systems (Synchronized product of systems, Mazurkiewicz traces or parallel series) can be specified within. Besides its general aspect, our model offers decidability results on the verification problem according to an MSO formula on pomsets.

This article describes first steps towards the formal specification and verification of multi-agent systems, through the use of temporal belief logics. The article first describes Concurrent METATEM, a multi-agent programming language, and then develops a logic that may be used to reason about Concurrent METATEM systems. The utility of this logic for specifying and verifying Concurrent METATEM systems is demonstrated through a number of examples. The article concludes with a brief discussion on the wider implications of the work, and in particular on the use of similar logics for reasoning about multi-agent systems in general.

We propose a collection of principles for reasoning about lazy functional programs. These include rules for predicate logic, rules of conversion of programs, and rules for predicates defined in terms of least and greatest fixed points. These rules can be used for reasoning about networks of deterministic computing agents in view of Kahn’s principle. We also propose that certain networks which include non-deterministic agents can be treated in a similar way by viewing such agents as incompletely specified deterministic agents. To illustrate this technique we discuss the specification and correctness of the alternating bit protocol.KeywordsRecursive FunctionPredicate LogicInput StreamFunctional ProgramNatural DeductionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Modal logics and behavioral equivalences play an important role in the specification and verification of concurrent systems. In this paper, we first present a new notion of bisimulation for nondeterministic fuzzy transition systems, which is distribution based and coarser than state-based bisimulation appeared in the literature. Then, we define a distribution-based bisimilarity metric as the least fixed point of a suitable monotonic function on a complete lattice, which is a behavioral distance and is a more robust way of formalizing behavioral similarity between states than bisimulations. We also propose an on-the-fly algorithm for computing the bisimilarity metric. Moreover, we present a fuzzy modal logic and provide a sound and complete characterization of the bisimilarity metric. Interestingly, this characterization holds for a class of fuzzy modal logics. In addition, we show the nonexpansiveness of a typical parallel composition operator with respect to the bisimilarity metric, which makes compositional verification possible.

On undecidability of propositional temporal logics on trace systems

Autonomous robotic systems are complex, hybrid, and often safety-critical; this makes their formal specification and verification uniquely challenging. Though commonly used, testing and simulation alone are insufficient to ensure the correctness of, or provide sufficient evidence for the certification of, autonomous robotics. Formal methods for autonomous robotics have received some attention in the literature, but no resource provides a current overview. This short paper summarises the contributions of Luckcuck 2019, which surveys the state-of-the-art in formal specification and verification for autonomous robotics.

We develop a logic-based framework for formal specification and algorithmic verification of homogeneous and dynamic concurrent multi-agent transition systems. Homogeneity means that all agents have the same available actions at any given state and the actions have the same effects regardless of which agents perform them. The state transitions are therefore determined only by the vector of numbers of agents performing each action and are specified symbolically, by means of conditions on these numbers definable in Presburger arithmetic. The agents are divided into controllable (by the system supervisor/controller) and uncontrollable, representing the environment or adversary. Dynamicity means that the numbers of controllable and uncontrollable agents may vary throughout the system evolution, possibly at every transition. As a language for formal specification we use a suitably extended version of Alternating-time Temporal Logic, where one can specify properties of the type “a coalition of (at least) n controllable agents can ensure against (at most) m uncontrollable agents that any possible evolution of the system satisfies a given objective gamma″, where gamma is specified again as a formula of that language and each of n and m is either a fixed number or a variable that can be quantified over. We provide formal semantics to our logic {mathcal {L}}_{textsc {hdmas}} and define normal form of its formulae. We then prove that every formula in {mathcal {L}}_{textsc {hdmas}} is equivalent in the finite to one in a normal form and develop an algorithm for global model checking of formulae in normal form in finite HDMAS models, which invokes model checking truth of Presburger formulae. We establish worst case complexity estimates for the model checking algorithm and illustrate it on a running example.

Formal specification and verification of complex IoT systems’ behavior can efficiently improve the systems’ correctness and reliability. This paper presents an enhanced time behavior protocol to specify real-time components’ timed interaction behaviors in IoT systems. The protocol model bound event tokens with time consumption constraint information according to requirements of practical applications, and time-related operators are added into the model language. Visualization and verification method for composited behavior is given. An application example is introduced, and the experimental results show that the enhanced time behavior protocol-based model can be used easily to specify, visualize, and verify IoT systems’ interaction behavior and timing constraint information.

In this paper we present our approach allowing the translation of Real Time Multi-Agents Systems (RT-MAS) organizational requirements described by extended AUML (Agent UML Language) diagrams into a formal specification written in Real Time Maude language (RT-Maude). In fact, the approach is an extension of our previous work [1] that consists in extending AUML diagrams (Temporal AUML organization use case diagram and Temporal AUML organization class diagram) by using stereotypes notions and meta-model organizations entities for taking into account RT-MAS specificities. Once elaborated, these different diagrams undergo a validation to assure inter-and intra model coherence. The formal and object oriented language RT-Maude, base on rewriting logic, supports formal specification and programming of concurrent systems. The main motivations of this work are: (1) formalizing the organizational requirements of RT-MAS by using RT-Maude language, and (2) integrating the validation of the coherence models, since the analysis phase.

International audience

Representation of scopes of names is important for analysis and verification of concurrent systems. However, it is difficult to represent the scopes of channel names precisely with models based on process algebra.We introduced a model of concurrent systems with higher-order communication based on graph rewriting in our previous work. A bipartite directed acyclic graph represents a concurrent system that consists of a number of processes and messages in that model. The model can represent the scopes of local names precisely. We defined an equivalence relation such that two systems are equivalent not only in their behavior, but also in extrusion of scopes of names. This paper shows that our equivalence relation is a congruence relation w.r.t. τ-prefix, new-name, replication and composition, even when higher-order communication is allowed. We also show our equivalence relation is not congruent w.r.t. input-prefix though it is congruent w.r.t. input-prefix in the first-order case.

Architectures based on Coordinated Atomic action (CA action) concepts have been used to build concurrent fault-tolerant systems. This conceptual model combines concurrent exception handling with action nesting to provide a general mechanism for both enclosing interactions among system components and coordinating forward error recovery measures. This paper proposes an architectural model to guide the formal specification of concurrent fault-tolerant systems. This architecture provides built-in CSP (Communicating Sequential Process) processes and predefined channels to coordinate exception handling of the user-defined components. As a result, a formal and general architecture supporting software fault-tolerance are ready to be used.

In protocol development for wireless systems, the choice of appropriate mobility models describing the movement patterns of devices has long been recognised as a crucial factor for the successful evaluation of protocols. More recently, wireless protocols have also come into the focus of formal approaches to the modelling and verification of concurrent systems. While in these approaches mobility is also given a central role, the actual mobility modelling remains simplistic since arbitrary node movements are allowed. This leads to a huge behavioural overapproximation that might prevent a successful reasoning about protocol properties. In this paper we describe how to extend a process calculus by realistic mobility models in an orthogonal way. The semantics of our calculus incorporates a notion of global time passing that allows us to express a wide range of mobility models currently used in protocol development practice. Using the behavioural equivalence and pre-order of our calculus, we are furthermore able to compare the strength of these models in our approach.

Formal Specification and Verification of System of Systems Using UPPAAL: A Case Study of a Defensive Missile Systems