Decision Problems for Petri Nets with Names

We prove several decidability and undecidability results for nu-PN, an extension of P/T nets with pure name creation and name management. We give a simple proof of undecidability of reachability, by reducing reachability in nets with inhibitor arcs to it. Thus, the expressive power of nu-PN strictly surpasses that of P/T nets. We prove that nu-PN are Well Structured Transition Systems. In particular, we obtain decidability of coverability and termination, so that the expressive power of Turing machines is not reached. Moreover, they are strictly Well Structured, so that the boundedness problem is also decidable. We consider two properties, width-boundedness and depth-boundedness, that factorize boundedness. Width-boundedness has already been proven to be decidable. We prove here undecidability of depth-boundedness. Finally, we obtain Ackermann-hardness results for all our decidable decision problems.Comment: 20 pages, 7 figure

On the decidability of model checking LTL fragments in monotonic extensions of Petri nets

We study the model checking problem for monotonic extensions of Petri Nets, namely for two extensions of Petri nets: reset nets (nets in which places can be emptied by the firing of a transition with a reset arc) and ν-Petri nets (nets in which tokens are pure names that can be matched with equality and dynamically created). We consider several fragments of LTL for which the model checking problem is decidable for P/T nets. We first show that for those logics, model checking of reset nets is undecidable. We transfer those results to the case of ν-Petri nets. In order to cope with these negative results, we define a weaker fragment of LTL, in which negation is not allowed. We prove that for that fragment, the model checking of both reset nets and ν-Petri nets is decidable, though with a non primitive recursive complexity. Finally, we prove that the model checking problem for a version of that fragment with universal interpretation is undecidable even for P/T nets

Mobile Synchronizing Petri Nets: A Choreographic Approach for Coordination in Ubiquitous Systems

AbstractThe term Ubiquitous Computing was coined by Mark Weiser almost two decades ago. Despite all the time that has passed since Weiser's vision, ubiquitous computing still has a long way ahead to become a pervasive reality. One of the reasons for this may be the lack of widely accepted formal models capable of capturing and analyzing the complexity of the new paradigm. We propose a simple Petri Net based model to study some of its main characteristics. We model both devices and software components as a special kind of coloured Petri Nets, located in locations, that can move to other locations and synchronize with other co-located nets, offering and requesting services. We obtain an amenable model for ubiquitous computing, due to its graphical representation. We present our proposal in a progressive way, first presenting a basic model where coordination is formalized by the synchronized firing of pairs of compatible transitions that offer and request a specific service, and ad hoc networks are modeled by constraining mobility by the dynamic acquisition of locality names. Next, we introduce a mechanism for the treatment of robust security properties, namely the generation of fresh private names, to be used for authentication properties

Ubiquitous systems and Petri nets

Several years before the popularization of the Internet, Mark Weiser proposed the concept of ubiquitous computing with the purpose of enhancing the use of computers by making many computers available throughout the physical environment, but making them effectively invisible to the user. Nowadays, such idea affects all areas of computing science, including both hardware and software. In this paper, a formal model for ubiquitous systems based on Petri nets is introduced and motivated with examples and applications. This simple model allows the definition of two-level ubiquitous systems, composed of a collection of processor nets providing services, and a collection of process nets requesting those services. The modeled systems abstract from middleware details, such as service discovery protocols, and security infrastructures, such as PKI’s or trust policies, but not from mobility or component compatibility

Validación en línea de aspectos formales y corrección asistida de ejercicios en asignaturas con evaluación continua

Depto. de Sistemas Informáticos y ComputaciónFac. de InformáticaFALSEsubmitte

Renovación del sistema de información docente de la Facultad de Informática

Memoria del proyecto Innova-Gestión 301 de la convocatoria 2019/2020 "Renovación del sistema de información docente de la Facultad de Informática" que consistía en la implementación de una primera versión de sistema de información interno para la gestión de horarios, fichas docentes, tutorías y otros datos relevantes para la docencia para ser utilizado en la facultad de informática

Basic completion strategies as another application of the Maude strategy language

The two levels of data and actions on those data provided by the separation between equations and rules in rewriting logic are completed by a third level of strategies to control the application of those actions. This level is implemented on top of Maude as a strategy language, which has been successfully used in a wide range of applications. First we summarize the Maude strategy language design and review some of its applications; then, we describe a new case study, namely the description of completion procedures as transition rules + control, as proposed by Lescanne.Comment: In Proceedings WRS 2011, arXiv:1204.531

Petri nets for the verification of Ubiquitous Systems with Transient Secure Association

Transient Secure Association has been widely accepted as a possible alternative to traditional authentication in the context of Ubiquitous Computing. In this paper we develop a formal model for the Resurrecting Duckling Policy that implements it. Our model, that we call TSA systems, is based on Petri Nets, thus obtaining an amenable graphical representation of our systems. We prove that TSA specifications have the same expressive power as P/T nets, so that coverability, that can be used to specify security properties in this setting, is decidable for TSA systems. Then we address the problem of implementing TSA systems with a lower level model that only relies on the secure exchange of secret keys. We prove that if we view these systems as closed systems then our implementation is still equivalent to P/T nets. However, if we consider an open framework then we need a mechanism of fresh name creation to get a correct implementation. This last model is not equivalent to P/T nets, but the coverability problem is still decidable for them, even in an open setting, so that checking the security properties of the represented systems remains decidable