Modeling Time in Computing: A Taxonomy and a Comparative Survey

The increasing relevance of areas such as real-time and embedded systems, pervasive computing, hybrid systems control, and biological and social systems modeling is bringing a growing attention to the temporal aspects of computing, not only in the computer science domain, but also in more traditional fields of engineering. This article surveys various approaches to the formal modeling and analysis of the temporal features of computer-based systems, with a level of detail that is suitable also for non-specialists. In doing so, it provides a unifying framework, rather than just a comprehensive list of formalisms. The paper first lays out some key dimensions along which the various formalisms can be evaluated and compared. Then, a significant sample of formalisms for time modeling in computing are presented and discussed according to these dimensions. The adopted perspective is, to some extent, historical, going from "traditional" models and formalisms to more modern ones.Comment: More typos fixe

Deciding the Satisfiability of MITL Specifications

In this paper we present a satisfiability-preserving reduction from MITL interpreted over finitely-variable continuous behaviors to Constraint LTL over clocks, a variant of CLTL that is decidable, and for which an SMT-based bounded satisfiability checker is available. The result is a new complete and effective decision procedure for MITL. Although decision procedures for MITL already exist, the automata-based techniques they employ appear to be very difficult to realize in practice, and, to the best of our knowledge, no implementation currently exists for them. A prototype tool for MITL based on the encoding presented here has, instead, been implemented and is publicly available.Comment: In Proceedings GandALF 2013, arXiv:1307.416

Non-null Infinitesimal Micro-steps: a Metric Temporal Logic Approach

Many systems include components interacting with each other that evolve with possibly very different speeds. To deal with this situation many formal models adopt the abstraction of "zero-time transitions", which do not consume time. These however have several drawbacks in terms of naturalness and logic consistency, as a system is modeled to be in different states at the same time. We propose a novel approach that exploits concepts from non-standard analysis to introduce a notion of micro- and macro-steps in an extension of the TRIO metric temporal logic, called X-TRIO. We use X-TRIO to provide a formal semantics and an automated verification technique to Stateflow-like notations used in the design of flexible manufacturing systems.Comment: 20 pages, 2 figures, submitted to the conference "FORMATS: Formal Modelling and Analysis of Timed Systems" 201

A timeband framework for modelling real-time systems

Complex real-time systems must integrate physical processes with digital control, human operation and organisational structures. New scientific foundations are required for specifying, designing and implementing these systems. One key challenge is to cope with the wide range of time scales and dynamics inherent in such systems. To exploit the unique properties of time, with the aim of producing more dependable computer-based systems, it is desirable to explicitly identify distinct time bands in which the system is situated. Such a framework enables the temporal properties and associated dynamic behaviour of existing systems to be described and the requirements for new or modified systems to be specified. A system model based on a finite set of distinct time bands is motivated and developed in this paper

A Theory of Sampling for Continuous-time Metric Temporal Logic

This paper revisits the classical notion of sampling in the setting of real-time temporal logics for the modeling and analysis of systems. The relationship between the satisfiability of Metric Temporal Logic (MTL) formulas over continuous-time models and over discrete-time models is studied. It is shown to what extent discrete-time sequences obtained by sampling continuous-time signals capture the semantics of MTL formulas over the two time domains. The main results apply to "flat" formulas that do not nest temporal operators and can be applied to the problem of reducing the verification problem for MTL over continuous-time models to the same problem over discrete-time, resulting in an automated partial practically-efficient discretization technique.Comment: Revised version, 43 pages

Définitions opérationnelles du temps pour l'analyse des données longitudinales : illustration dans le champ des mobilités spatiales

International audienceTemporality of human and social phenomena raises theoretical complex issues and specific technical challenges, including analyzing and visualizing of temporal information. This paper proposes an operational typology of three kinds of time: schedule-time, process-time and succession-time. Then it illustrates the usefulness of this typology through three case studies dealing with mobility (residential trajectories, programs of activities and daily trips, routes of freight delivery). These examples are analyzed using longitudinal data and several modes of graphical representation (distribution plot, sequence frequency plot, slide plot). Our approach is willing to enrich and clarify the understanding of time as an attribute into a statistical information system. This approach is inductive and pragmatic: we started with specific thematic and technical issues regarding the analysis and the graphical representation of longitudinal data to move towards theoretical specifications of time. In short, we tried to model an appropriate time to our research objects. This research approach is rendered in reverse in the article: from the theoretical thinking about time to the field of spatial mobility.La temporalité des phénomènes étudiés en sciences humaines et sociales pose des problèmes théoriques complexes et des problèmes techniques spécifiques, notamment d'analyse et de visualisation de l'information temporelle. Cet article propose une typologie opérationnelle distinguant trois types de temps – calendrier, processus et succession – puis il illustre l'intérêt de cette typologie à travers trois cas d'étude qui traitent des mobilités spatiales (parcours résidentiels, programmes d'activités et de déplacements quotidiens, itinéraires d'acheminement de marchandises). Ces exemples sont analysés à partir de données longitudinales et de plusieurs modes de représentation graphique (en chronogramme, en tapis, en coulées). Nous cherchons ainsi à enrichir et clarifier l'appréhension du temps comme attribut dans un système d'information statistique. Notre démarche de recherche a été largement inductive et pragmatique. Nous sommes partis de préoccupations thématiques et techniques particulières, concernant l'analyse et la représentation graphique des données longitudinales, pour aller vers des spécifications théoriques plus générales du temps. Nous avons cherché, en somme, à modeler un temps à la mesure de nos objets de recherche. Cette démarche est restituée en sens inverse dans l'article : de la réflexion théorique à la mise en pratique dans le champ des mobilités spatiales

Specifying time-sensitive systems with TLA+

International audienceWe present a pattern-based method to express time specifications in the language TLA+. A real-time module RealTimeNew is introduced to encapsulate the definitions of commonly used time patterns. We present a general framework to differentiate the temporal characterizations from system functionality with time constraints. The temporal specification is concise and provably as a refinement of its corresponding functional description without time. The method ameliorates the usability of TLA+ in specifying and verifying time-sensitive systems. A case study is harnessed to illustrate and validate the approach

Statistical Model Checking of Human-Robot Interaction Scenarios

Robots are soon going to be deployed in non-industrial environments. Before society can take such a step, it is necessary to endow complex robotic systems with mechanisms that make them reliable enough to operate in situations where the human factor is predominant. This calls for the development of robotic frameworks that can soundly guarantee that a collection of properties are verified at all times during operation. While developing a mission plan, robots should take into account factors such as human physiology. In this paper, we present an example of how a robotic application that involves human interaction can be modeled through hybrid automata, and analyzed by using statistical model-checking. We exploit statistical techniques to determine the probability with which some properties are verified, thus easing the state-space explosion problem. The analysis is performed using the Uppaal tool. In addition, we used Uppaal to run simulations that allowed us to show non-trivial time dynamics that describe the behavior of the real system, including human-related variables. Overall, this process allows developers to gain useful insights into their application and to make decisions about how to improve it to balance efficiency and user satisfaction.Comment: In Proceedings AREA 2020, arXiv:2007.1126

SAFER-HRC: Safety analysis through formal vERification in human-robot collaboration

Whereas in classic robotic applications there is a clear segregation between robots and operators, novel robotic and cyber-physical systems have evolved in size and functionality to include the collaboration with human operators within common workspaces. This new application field, often referred to as Human-Robot Collaboration (HRC), raises new challenges to guarantee system safety, due to the presence of operators. We present an innovative methodology, called SAFER-HRC, centered around our logic language TRIO and the companion bounded satisfiability checker Zot, to assess the safety risks in an HRC application. The methodology starts from a generic modular model and customizes it for the target system; it then analyses hazards according to known standards, to study the safety of the collaborative environment