Fernando Tricas

University of Zaragoza | UNIZAR · Department of Computing and Systems Engineering

Petri Nets are graph based tools to model and study concurrent systems and their properties; one of them is liveness, which is related to the possibility of every part of the system to be activated eventually. Siphons are sets of places that have been related to liveness properties. When we need to deal with realistic problems its computation is ha...

Petri net based methodological approaches in deadlock prevention are a success story in the domain of Flexible Manufacturing Systems (FMSs). Along the years, diverse Petri net classes for dealing with the so-called Resource Allocation Problem (RAP) have emerged in the field. These are usually derived from the physical constraints of different plant...

In this paper a novel article ranking method called NectaRSS is introduced. The system recommends incoming articles, which we will designate as newsitems, to users based on their past choices. User preferences are automatically acquired, avoiding explicit feedback, and ranking is based on those preferences distilled to a user profile. NectaRSS uses...

Weblogs are dynamic websites updated via easy-to-use content management systems and organized as a set of chronologically ordered stories, frequently built around a link or including links to other weblogs. Since they are managed by individuals, their links tend to mirror or, in some cases, establish new types of social relations, thereby creating...

Siphons are related to the liveness properties of Petri net models. This relation is strong in the case of resource allocation systems (RASs). Siphons can be used in these systems in order to both characterize and prevent/avoid deadlock situations. However, the computation of these structural components can be very time consuming or, even, impossib...

Resumen-Internet ha cambiado la práctica de la investigación. Un investigador del siglo XXI debe tener presencia en el ecosistema digital propio de la Ciencia Abierta. Esta presencia va a ocurrir con independencia de que el investigador lo quiera o no, pero si se es consciente de ello y además se abren los perfiles adecuados en los servicios más pu...

Creating rankings might seem like a vain exercise in belly-button gazing, even more so for people so unlike that kind of things as programmers. However, in this paper we will try to prove how creating city (or province) based rankings in Spain has led to all kind of interesting effects, including increased productivity and community building. We de...

Deadlock states are undesirable situations in any system,. Their avoiding presents a major issue in control of resource allocation systems (RAS), a theoretical paradigm, used in construction of e.g. flexible manufacturing systems. In coordinating RAS with processes containing concurrent execution in their development, it has been proved, that deadl...

Petri nets are graph based tools to model and study concurrent systems and their properties; one of them is liveness, which is related to the possibility of every part of the system to be activated eventually. Siphons are sets of places that are related to liveness properties. When we need to deal with realistic problems its computation is hard or...

Deaddlock states are undesirable situations in any system. Their avoiding presents a major issue in control of resource allocation systems (RAS), a theoretical paradigm used in construction of several application systems, including flexible manufacturing systems. In coordinating RAS with non-sequential processes, i.e. processes containing concurren...

The disparity of Petri net models in the literature for the study of resource allocation problems in Flexible Manufacturing Systems (FMSs) is overwhelming. Paradoxically, those models often strongly overlap in terms of their modeling capability. Such clustering seems to be impelled by a mature knowledge of results which capsize liveness at the topo...

COSMOS, Computer Science for Complex System Modeling, is a research team that has the mission of bridging the gap between formal methods and real problems. The goal is twofold: (1) a better management of the growing complexity of current systems; (2) a high quality of the implementation reducing the time to market. The COSMOS vision is to prove thi...

Some utlities to create different types of Petri Net models Code available at: https://github.com/fernand0/Petri-Net-tools

Social media is increasingly a part of our life. This is also the case for our students: most of them have Facebook, some of them have a Twitter account and they are more and more accustomed to these tools and others so it makes sense to try to integrate some of them in our teaching routines: the class is not only a place, but a set of resources av...

El propósito de este trabajo es generalizar y extender los resultados existentes en el análisis, prevención y evitación de bloqueos en sistemas de asignación de recursos, con una atención especial hacia los sistemas de fabricación flexible. En este sentido, se proponen nuevas clases de sistemas con restricciones similares a las que podemos encontra...

In this paper the utility of using the Self Organizing Maps (SOM), in conjunction with U-matrix, to visualize the evolution of a social network community formed by a set of blogs is shown. Weblogs are dynamic websites updated via easy-to-use content management systems whose links tend to mirror or in some cases establish new types of social relatio...

The challenge of ad-hoc computing is to find the way of taking advantage of spare cycles in an efficient way that takes into account all capabilities of the devices and interconnections available to them. In this paper we explore distributed evolutionary computation based on the Ruby on Rails framework, which overlays a Model-View-Controller on evo...

Weblogs are web sites where one or several authors publish their opinions about current events. Even in Spain, there are several thousands, and it is often difficult to find a weblog that meets one's interest. Recommendation services thus become, if not a need, at least a convenience. In this paper we propose automatic extraction of association rul...

Introducción En los días transcurridos entre el atentado del 11M y las elecciones del 14M se vivió en España un intenso debate en torno a la autoría de los atentados que tuvo una incidencia difícil de determinar en las elecciones. Un debate cuyo punto de partida, a su vez, constó de dos condicionantes principales: primero, las diferentes estrategia...

A new method for the deadlock prevention problem in concurrent systems where a set of processes share a set of common resources in a conservative way is proposed. The proposed approach can be applied to flexible manufacturing systems, modeled with Petri nets. The class of systems we will deal with eliminates some constraints imposed in previous re-...

A new method for the deadlock prevention problem in concurrent systems where a set of processes share a set of common resources in a conservative way is proposed. It can be applied to flexible manufacturing systems, modeled with Petri nets. In this paper, we present a set of important results related to the deadlock prevention problem in S<sup>4</s...

El estudio cuantitativo del tamaño y de las relaciones propias de la blogosfera hispana nos ayuda a comprender mejor el fenómeno blog en el ámbito de las lenguas hispanas, hasta ahora no muy bien representado en los estudios internacionales, centrados habitualmente en la blogosfera angloparlante. Una de las principales conclusiones es que su tamaño...

Websites of a particular class form increasingly complex networks, and new tools are needed to map and understand them. A way of visualizing this complex network is by mapping it. A map highlights which members of the community have similar interests, and reveals the underlying social network. In this paper, we will map a network of websites using...

Siphons are related to liveness properties of Petri net models. This relation is strong in the case of resource allocation systems (RAS). Siphons can be used in these systems in order to both, characterize and prevent/avoid deadlock situations. However, the computation of these structural components can be very time consuming or, even, impossible....

The blogosphere is the community of bloggers, people or collectives who share information and opinions ordered chronologically. The Spanish-speaking blogo-sphere contains several thousand blogs; despite its small size, compared to the English-speaking (or maybe global) blogosphere, its characteristics are a bit dif-ferent. In general, it could be s...

This work concentrates on deadlock problems in concurrent systems due to the common use of system resources organized in what is commonly known as Sequential Resource Allocation Systems and paying a special attention to subclasses of manufacturing systems. To do that, special classes of Petri net models are defined that allow to capture resource al...

Banker's-like approaches to deadlock avoidance are based on a decision procedure to grant active processes resources using information about the maximum needs of resources that a process can request in order to ensure termination. The paper presents an extension of the classical Banker's algorithm to a class of flexible manufacturing systems modele...

Linear descriptions of the set of reachable markings are used in conjunction with linear algebraic techniques to analyze properties of net systems, avoiding the state explosion problem. But they have a major problem: the spurious solutions. On the contrary of the general case, for Structurally Safe Net Systems it is always possible to remove all th...

In [F. Tricas, J. Colom and J. Ezpeleta, “A solution to the problem of deadlocks in concurrent system using Petri nets and integer linear programming”, in: G. Horton, D. Moller and U. Rude (eds.), Proc. of the 11th European Simulation Symposium, 542–546, (1999)], we presented a new method for deadlock prevention in flexible manufacturing systems us...

When a set of processes must share a set of common resources, deadlock problems can arise. To face them, three approaches are usually applied: deadlock detection and recovery, deadlock prevention or deadlock avoidance. In this paper we present one prevention and two avoidance deadlock algorithms for a class of models that appear in manufacturing sy...

The paper presents two methods for deadlock avoidance in concurrent systems. We apply the proposed approaches to flexible manufacturing systems, modeled by means of Petri nets. Both methods correspond to improvements of the classical Banker's algorithm, and are based on the knowledge of the process structure. The first one is polynomial in the size...

The paper presents a new method for the deadlock problem in concurrent systems where a set of processes share a set of common resources. We apply the proposed approach to flexible manufacturing systems, modeled by means of Petri Nets. This approach is based in the structural components of the Petri nets, mainly in siphons. The problem is solved for...

In this paper we introduce a new control policy for a class of nets that appear in the modeling of flexible manufacturing systems. Both the model of the system and its control are established by using Petri nets. The aim of the imposed control as to ensure that no deadlock problem can occur in the controlled system: a deadlock implies that the proc...

In this paper we propose a method for the design of the control of Discrete Event Systems (DES) modelled by Petri nets. In this context, the specification of the forbidden states and its manipulation is the fundamental problem, because of the large size of the state spaces of DESs. We propose the use of Ordered Binary Decision Diagrams (OBDDs) to o...

In the modelling and control of manufacturing systems one of the aims is to obtain a system that can run in an automatic way. This means that the software in charge of the monitoring and control of the system must be able to deal with a set of problematic situations (system failures, system deadlocks, overflow of storing facilities, etc.). In this...

To deal with the complexity of the implementation of control systems for flexible manufacturing systems, formal methods of design are needed. In this work the modeling and validation tool selected is high level Petri nets. Based on this approach we have studied the problems that a distributed implementation can introduce. For the evaluation of diff...

The design of concurrent systems has to deal with the satisfaction of conditions of good behavior. In this work the way to model and analyze concurrent systems is using a subclass of Petri nets that is an extension of a previous class studied for the same kind of problems. Starting from a Petri net that models a system a policy is proposed to elimi...

To deal with the complexity of the implementation of control systems for flexible manufacturing systems formal methods of design are needed. In this work the modelling and validation tool selected is high level Petri nets. Based on this approach we have studied the problems that a distributed implementation can produce. For the evaluation of differ...

The design of concurrent systems has to deal with the satisfaction of conditions of good behavior. In this work the way to model and analyze concurrent systems is using a subclass of Petri nets that is an extension of a previous class studied for the same kind of problems. Starting from a Petri net that models a system a policy is proposed to elimi...

This paper will present how weblogs, or web-based, chronologically-ordered, content management system, can be used as part of computer science classes. The experience consisted in having the class professor use a weblog for class-related topics, as well as anything mentioned in class that needed the complement of a hyperlink, and giving students th...

In the modeling and control of manufacturing systems one of the aims is to obtain a system that can run in an automatic way. This means that the software in charge of the monitoring and control of the system must be able to deal with a set of problematic situations (system failures, system deadlocks, overrow of storing facilities, etc.). In this pa...

The blogosphere is the community of bloggers, people or collectives who share information and opinions ordered chronologically. The Spanish-speaking blogosphere contains several thousand blogs; despite its small size, compared to the English-speaking (or maybe global) blogosphere, its characteristics are a bit different. During the last months the...

Web-based communities, such as those created around weblogs, form increasingly complex networks, and new tools are needed to map and understand them. Creating a community map allows the visualization of community standing and relationship, and it can be used to discover which members of the community have similar interests. Since hyperlinks are an...

Docencia 2.0, ¿Universidad 2.0? El término web 2.0 fue introducido por Tim O'Reilly en el año 2004 con el objetivo de etiquetar la segunda generación de la web y la forma de interaccionar del usuario con ella. En ese momento, las herramientas disponibles para gestionar sitios web habían evolucionado lo suficiente como para poner en manos de un grup...

Weblogs or blogs are a new form of diffusion of content and knowledge. They can be, and have been, used for different matters ranging from the expression of the angst of adolescent people (which has been used in some ocasions to dismiss the value of the whole phenomenon) to the diffusion of higher-level knowledge available in some areas of research...

RESUMEN La introducción de herramientas TIC en una clase con conexí on permanente a Internet suele aumentar la participación por parte del alumno en la asignatura, y por ello, nos sentimos motivados para la búsqueda de un CMS (o sistema gestor de contenidos) que centralizara esfuerzos y facilitara el seguimiento tanto virtual como presencial de las...