Safraless Synthesis for Epistemic Temporal Specifications

2005

Multi-agent systems (MAS) are a successful paradigm employed in the formalisation of many scenarios [30, 31], including communication protocols, security protocols, autonomous planning, etc. In many instances, MAS are modelled by means of multi-modal logics with modal operators to reason about temporal, epistemic, doxastic, and other properties of agents. As MAS being modelled grow larger, however, automatic techniques are crucially required for the formal verification of MAS specification.

Journal of Logic, Language and Information, 2010

We suggest that developing automata theoretic foundations is relevant for knowledge theory, so that we study not only what is known by agents, but also the mechanisms by which such knowledge is arrived at. We define a class of epistemic automata, in which agents' local states are annotated with abstract knowledge assertions about others. These are finite state agents who communicate synchronously with each other and information exchange is 'perfect'. We show that the class of recognizable languages has good closure properties, leading to a Kleene-type theorem using what we call regular knowledge expressions. These automata model distributed causal knowledge in the following way: each agent in the system has a partial knowledge of the temporal evolution of the system, and every time agents synchronize, they update each other's knowledge, resulting in a more up-to-date view of the system state. Hence we show that these automata can be used to solve the satisfiability problem for a natural epistemic temporal logic for local properties. Finally, we characterize the class of languages recognized by epistemic automata as the regular consistent languages studied in concurrency theory.

ArXiv, 2019

The distributed temporal logic DTL is a logic for reasoning about temporal properties of distributed systems from the local point of view of the system's agents, which are assumed to execute sequentially and to interact by means of synchronous event sharing. Different versions of DTL have been provided over the years for a number of different applications, reflecting different perspectives on how non-local information can be accessed by each agent. In this paper, we propose a novel notion of distributed Buchi automaton envisaged to encompass DTL with a model-checking mechanism.

2004

This paper addresses the problem of verification of temporal epistemic properties of multi-agent systems by means of symbolic model checking. An overview of the technique of bounded model checking for temporal epistemic logic, and an analysis of some limitations of the method are provided. An extension of this technique called unbounded model checking to solve these limitations is explored. Similarities and differences of the two methods are explicitly exemplified by the analysis of a scenario in the two formalisms.

Electronic Proceedings in Theoretical Computer Science, 2018

The paper is focused on temporal logics for the description of the behaviour of real-time pushdown reactive systems. The paper is motivated to bridge tractable logics specialized for expressing separately dense-time real-time properties and context-free properties by ensuring decidability and tractability in the combined setting. To this end we introduce two real-time linear temporal logics for specifying quantitative timing context-free requirements in a pointwise semantics setting: Event-Clock Nested Temporal Logic (EC NTL) and Nested Metric Temporal Logic (NMTL). The logic EC NTL is an extension of both the logic CaRet (a context-free extension of standard LTL) and Event-Clock Temporal Logic (a tractable real-time logical framework related to the class of Event-Clock automata). We prove that satisfiability of EC NTL and visibly model-checking of Visibly Pushdown Timed Automata (VPTA) against EC NTL are decidable and EXPTIME-complete. The other proposed logic NMTL is a context-free extension of standard Metric Temporal Logic (MTL). It is well known that satisfiability of future MTL is undecidable when interpreted over infinite timed words but decidable over finite timed words. On the other hand, we show that by augmenting future MTL with future context-free temporal operators, the satisfiability problem turns out to be undecidable also for finite timed words. On the positive side, we devise a meaningful and decidable fragment of the logic NMTL which is expressively equivalent to EC NTL and for which satisfiability and visibly model-checking of VPTA are EXPTIME-complete. * The work by Adriano Peron and Aniello Murano has been partially supported by the GNCS project Formal methods for verification and synthesis of discrete and hybrid systems and by Dept. project MODAL MOdel-Driven Analysis of Critical Industrial Systems.

1997

We describe an automata-theoretic approach to the automated checking of truth and validity for temporal logics. The basic idea underlying this approach is that for any formula we can construct an alternating automaton that accepts precisely the models of the formula. For linear temporal logics the automaton runs on infinite words while for branching temporal logics the automaton runs on infinite trees.

Adaptive Agents and Multi-Agents Systems, 2016

Temporal Epistemic Logic is used to reason about the evolution of knowledge over time. A notable example is the temporal epistemic logic KL1, which is used to model what a reasoner can infer about the state of a dynamic system by using available observations. Applications of KL1 span from security (verification of cryptography protocols and information flow) to diagnostic systems (fault detection and diagnosability). In this paper, we tackle the verification of KL1 properties under observational semantics, by proposing an effective approach that is able to deal with both finite and infinite state systems. The denotation of the epistemic atoms is computed in a lazy way, driven by the counterexamples obtained from model checking an abstraction of the property. We analyze the approach on a comprehensive set of finite-and infinite-state benchmarks from the literature, evaluate the effectiveness of various optimizations, and demonstrate that our approach outperforms existing approaches.

1998

Compositional verification aims at managing the complexity of the verification process by exploiting compositionality of the system architecture. In this paper we explore the use of a temporal epistemic logic to formalize the process of verification of compositional multi-agent systems. The specification of a system, its properties and their proofs are of a compositional nature, and are formalized within a compositional temporal logic: Temporal Multi-Epistemic Logic. It is shown that compositional proofs are valid under certain conditions. Finally, the possibility of incorporating default persistence of information in a system, is explored.

Hardware and Software: Verification and Testing, 2017

Temporal synthesis is the automated design of a system that interacts with an environment, using the declarative specification of the system's behavior. A popular language for providing such a specification is Linear Temporal Logic, or LTL. LTL synthesis in the general case has remained, however, a hard problem to solve in practice. Because of this, many works have focused on developing synthesis procedures for specific fragments of LTL, with an easier synthesis problem. In this work, we focus on Safety LTL, defined here to be the Until-free fragment of LTL in Negation Normal Form (NNF), and shown to express a fragment of safe LTL formulas. The intrinsic motivation for this fragment is the observation that in many cases it is not enough to say that something "good" will eventually happen, we need to say by when it will happen. We show here that Safety LTL synthesis is significantly simpler algorithmically than LTL synthesis. We exploit this simplicity in two ways, first by describing an explicit approach based on a reduction to Horn-SAT, which can be solved in linear time in the size of the game graph, and then through an efficient symbolic construction, allowing a BDD-based symbolic approach which significantly outperforms extant LTL-synthesis tools.

2009

We introduce a symmetry reduction technique for model checking temporal-epistemic properties of multi-agent systems defined in the mainstream interpreted systems framework. The technique, based on counterpart semantics, aims to reduce the set of initial states that need to be considered in a model. We present theoretical results establishing that there are neither false positives nor false negatives in the reduced model. We evaluate the technique by presenting the results of an implementation tested against two well known applications of epistemic logic, the muddy children and the dining cryptographers. The experimental results obtained confirm that the reduction in model checking time can be dramatic, thereby allowing for the verification of hitherto intractable systems.