Fernando Tricas

Publications

• Visualizing the evolution of a web-based social network.

  Beatriz Prieto, Fernando Tricas, Juan Julián Merelo Guervós, Antonio Mora García, Alberto Prieto

  J. Network and Computer Applications. 01/2008; 31:677-698.

• Browser-based distributed evolutionary computation: performance and scaling behavior

  J. J. Merelo, Antonio Mora-Garcia, J. L. J. Laredo, Juan Lupion, Fernando Tricas

  02/2007;

  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 framew... [more] 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 evolutionary computation. It allows anybody with a web browser (that is, mostly everybody connected to the Internet) to participate in an evolutionary computation experiment. Using a straightforward farming model, we consider different factors, such as the size of the population used. We are mostly interested in how they impact on performance, but also the scaling behavior when a non-trivial number of computers is applied to the problem. Experiments show the impact of different packet sizes on performance, as well as a quite limited scaling behavior, due to the characteristics of the server. Several solutions for that problem are proposed.

• Analyzing a Web-Based Social Network Using Kohonen's SOM.

  Beatriz Prieto, Juan J. Merelo Guervós, Alberto Prieto, Fernando Tricas

  Computational and Ambient Intelligence, 9th International Work-Conference on Artificial Neural Networks, IWANN 2007, San Sebastián, Spain, June 20-22, 2007, Proceedings; 01/2007
• 2.03

  Impact points

  Computing minimal siphons in Petri net models of resource allocation systems: a parallel solution

  F. Tricas, J. Ezpeleta

  Systems, Man and Cybernetics, Part A: Systems and Humans, IEEE Transactions on. 06/2006;

  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 compon... [more] 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, impossible. Moreover, if, in general, the complete enumeration of the set of minimal siphons must be avoided (there can exist an exponential number of such components), some deadlock prevention methods rely on its (complete or partial) computation and enumeration. The special syntactical constraints of some classes of RASs can help in developing specific algorithms to compute siphons in a more efficient way. In this work, a known method for siphon computation is adapted to get advantage of the special (syntactical) structure of a class of RASs; a parallel implementation is proposed and some experimental results are presented

• A Petri Net Structure– Based Deadlock Prevention Solution for Sequential Resource Allocation Systems

  F. Tricas, F. Garcia-Valles, J.M. Colom, J. Ezpeleta

  Robotics and Automation, 2005. ICRA 2005. Proceedings of the 2005 IEEE International Conference on; 05/2005

  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 relate... [more] 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 S⁴PR nets. First, a liveness characterization is introduced, establishing how deadlocks can be studied in terms of circular waits. Second, we show how a circular wait situation corresponds to a particular marking related to a siphon of the Petri net model. Finally, this last characterization is used to obtain an iterative method that successively forbids deadlock related states, synthesizing the control necessary to ensure a final live behavior. The method can be implemented by means of the solutions of a set of integer linear programming problems.

• Mapping weblog communities

  Juan-J. Merelo-Guervos, Beatriz Prieto, Fatima Rateb, Fernando Tricas

  01/2004;

  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 th... [more] 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 Kohonen's self-organizing map (SOM), a neural-net like method generally used for clustering and visualization of complex data sets. The set of websites considered has been the Blogalia weblog hosting site (based at http://www.blogalia.com/), a thriving community of around 200 members, created in January 2002. In this paper we show how SOM discovers interesting community features, its relation with other community-discovering algorithms, and the way it highlights the set of communities formed over the network.

• Some results on siphon computation for deadlock prevention in resource allocation systems modeled with Petri nets

  F. Tricas, J. Ezpeleta

  Emerging Technologies and Factory Automation, 2003. Proceedings. ETFA '03. IEEE Conference; 10/2003

  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... [more] 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. Moreover, if, in general, the complete enumeration of the set of minimal siphons must be avoided (there can exist an exponential number of such components), some deadlock prevention methods rely on its (complete or partial) computation and enumeration. In the paper we show how the special syntactical constraints of some classes of resource allocation systems (we concentrate on S⁴PR) can help in developing specific implementations to compute siphons in a very efficient way.

• A Banker's solution for deadlock avoidance in FMS with flexible routing and multiresource states

  J. Ezpeleta, F. Tricas, F. Garcia-Valles, J.M. Colom

  Robotics and Automation, IEEE Transactions on. 09/2002;

  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 alg... [more] 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 modeled by means of Petri nets. These systems have two interesting characteristics from the application point of view. First, flexible routing of parts is allowed, and second, a multiset of resources is allowed to be used at each processing step. The decision procedure introduced is polynomial in the Petri net model size.

• New Methods for Deadlock Prevention and Avoidance in Concurrent Systems

  F. Tricas, J.M. Colom, J. Ezpeleta

  08/2000;

  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... [more] 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 systems. We use Petri nets as the tool for both, modelling and controlling the system. The prevention algorithm is based on an intensive use of the structure of the Petri net model. The avoidance algorithms correspond to improvements to the well-known Banker's algorithm introduced by Dijkstra in the framework of Operating Systems. 1 Introduction In [1] we proposed a new method for deadlock prevention in Flexible Manufacturing Systems (FMS). To do that, we modelled the manufacturing system by means of a class of Petri nets that we called S 4 PR. One of such nets is composed of a set of state machines (one per type of part to be processed in ...

• Some improvements to the Banker's algorithm based on the process structure

  F. Tricas, J.M. Colom, J. Ezpeleta

  Robotics and Automation, 2000. Proceedings. ICRA '00. IEEE International Conference on; 02/2000

  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 proc... [more] 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 of the Petri net model. The second one depends strongly on the number of alternative paths for the processing of parts and can be of a non-polynomial cost

• A Petri net solution to the problem of deadlocks in systems of processes with resources

  F. Tricas, J. Ezpeleta

  Emerging Technologies and Factory Automation, 1999. Proceedings. ETFA '99. 1999 7th IEEE International Conference on; 02/1999

  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 c... [more] 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 processing of some parts, once started, cannot be finished. This is a bad property for automated production systems. In the paper we use the structure of the Petri net model in order to characterize and solve the deadlock situations. We also present an experimental comparison between the proposed control policy and others that solve the same problem

• An extension of the liveness theory for concurrent sequential processes competing for shared resources

  F. Tricas, J. Martinez

  Systems, Man and Cybernetics, 1995. Intelligent Systems for the 21st Century., IEEE International Conference on; 11/1995

  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 ... [more] 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 eliminate deadlocked states

• Métrica de la blogosfera. Algunas medidas y relaciones en la blogosfera hispana

  Juan J. Merelo, Fernando Tricas

  Telos: Cuadernos de comunicación, tecnología y sociedad, ISSN 0213-084X, Nº. 65, 2005, pags. 101-104.

  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. Un... [more] 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 (medido en número de bitácoras) ha crecido de forma exponencial

• Visualizing the evolution of a web-based social network

  Beatriz Prieto, Fernando Tricas, Juan J. Merelo, Antonio Mora, Alberto Prieto

  Journal of Network and Computer Applications.

  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, establis... [more] 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 a social network. Studying the evolution of this network allows the discovery of emerging social structures and their growth trends. In this paper, we demonstrate the advantages of using the self-organizing maps (SOM) to visualize the evolution of a social network formed by a set of blogs, from their beginning to their current state. By observing the position a weblog is mapped to, it is easy to see what communities it belongs to nowadays, and how and when it became a part of those communities. The proposed procedure gives some insight on how communities are formed and have evolved. In this study, we apply this method to Blogalia, a blog-hosting site from which we have obtained a complete set of data and, by using SOM projections, we have drawn some conclusions on what drives the evolution of its implicit social network.

• Análisis, prevención y evitación de bloqueos en sistemas secuenciales de asignación de recursos

  Fernando Tricas García

  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 ... [more] 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 encontrar dentro del ámbito de los sistemas de fabricación. En un primer paso se estudiarán las propiedades estructurales de estas clases para comprobar que son adecuadas para el modelado y análisis del tipo de problemas considerado. Las soluciones al problema de los bloqueos se presentarán desde dos puntos de vista: prevención y evitación de los problemas de bloqueo, junto con algunos datos comparativos con otras soluciones al problema. El objetivo es obtener políticas de control muy permisivas, que puedan implantarse según diferentes consideraciones, proporcionando flexibilidad al diseñador del sistema. Finalmente se propone una mejora de un método de cálculo de cerrojos. Estas componentes estructurales están ligadas a la existencia de problemas de bloqueo en algunas clases de sistemas, y en ese sentido es muy conveniente disponer de métodos eficientes para su cálculo. El método propuesto mejora a los existentes mediante la utilización de paralelismo, y la adaptación a las características de los sistemas considerados. ----- 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 allocation events used to synchronize processes that have to share a set of reusable system resources. The classes of Petri nets introduced are studied from the structure point of view, showing the clear mapping among system and model structures. It is also shown how deadlock related situations can be explained in terms of markings and model structures. To solve deadlock problems, two different approaches are adopted. The first one is known as a deadlock prevention perspective, and makes an intensive use of different liveness characterizations developed in this work. The final result is a deadlock prevention algorithm that iteratively constrains the language of the input model so that the final controlled model is live in terms of Petri net definitions, which implies that the controlled system is free of deadlocks and ensures that the execution of any active process can terminate. The second approach falls into the deadlock avoidance family of solutions. In this work it is shown how the specific characteristics of the class of systems in consideration can be used to extend and improve the well-known Banker's solution for deadlock avoidance, allowing us to give a solution to deadlock problems in the most general class of sequential resource allocation systems. In both cases, and taking into account that obtaining the most permissive solution is NP-complete, the proposed solutions are experimentally compared with other solutions in order to get insight of how permissive the proposed algorithms are, showing they provide a good trade-off between computation cost and permissiveness.

• Deadlock Analysis, Prevention and Avoidance in Sequential Resource Allocation Systems

  Fernando Tricas

  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 ... [more] 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 encontrar dentro del ámbito de los sistemas de fabricación. En un primer paso se estudiarán las propiedades estructurales de estas clases para comprobar que son adecuadas para el modelado y análisis del tipo de problemas considerado. Las soluciones al problema de los bloqueos se presentarán desde dos puntos de vista: prevención y evitación de los problemas de bloqueo, junto con algunos datos comparativos con otras soluciones al problema. El objetivo es obtener políticas de control muy permisivas, que puedan implantarse según diferentes consideraciones, proporcionando flexibilidad al diseñador del sistema. Finalmente se propone una mejora de un método de cálculo de cerrojos. Estas componentes estructurales están ligadas a la existencia de problemas de bloqueo en algunas clases de sistemas, y en ese sentido es muy conveniente disponer de métodos eficientes para su cálculo. El método propuesto mejora a los existentes mediante la utilización de paralelismo, y la adaptación a las características de los sistemas considerados. ------- 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 allocation events used to synchronize processes that have to share a set of reusable system resources. The classes of Petri nets introduced are studied from the structure point of view, showing the clear mapping among system and model structures. It is also shown how deadlock related situations can be explained in terms of markings and model structures. To solve deadlock problems, two different approaches are adopted. The first one is known as a deadlock prevention perspective, and makes an intensive use of different liveness characterizations developed in this work. The final result is a deadlock prevention algorithm that iteratively constrains the language of the input model so that the final controlled model is live in terms of Petri net definitions, which implies that the controlled system is free of deadlocks and ensures that the execution of any active process can terminate. The second approach falls into the deadlock avoidance family of solutions. In this work it is shown how the specific characteristics of the class of systems in consideration can be used to extend and improve the well-known Banker's solution for deadlock avoidance, allowing us to give a solution to deadlock problems in the most general class of sequential resource allocation systems. In both cases, and taking into account that obtaining the most permissive solution is NP-complete, the proposed solutions are experimentally compared with other solutions in order to get insight of how permissive the proposed algorithms are, showing they provide a good trade-off between computation cost and permissiveness.

• Qué son las bitácoras y algunos datos sobre ellas

  Fernando Tricas García, Juan Julián Merelo Guervós

  El ecosistema digital, 2005-01-01, ISBN 84-370-6302-7, pags. 89-107.