## Virtual (and Real) World Ontology Services

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Un artículo interesante sobre el desarrollo de ontologías para modelar objetos del mundo real que es directamente aplicable a entornos virtuales 3D (metaversos), como Scond Life, Unity, OpenSim y muchos otros. Justamente fué el tema de mi charla en el II Congreso Metaversos hace un par de años: Metaversos semánticos.

Si a alguien le interesa este tema es otro de los posibles trabajos para AIWS, mi asignatura del máster IARFID.

Resumen
Augmented reality and virtual world applications both need to model semantic knowledge about real or virtual world objects. The current generation of virtual world platforms provides limited facilities for representing this kind of knowledge but a next generation will provide the means to tie semantic information to general or application-specific ontology services. This paper motivates the need for ontology services, outlines several approaches for associating ontology concepts with objects and locations, and discusses means to populate common sense ontologies from data harvested from the real and virtual worlds.

Acceso al artículo en computer.org (de pago)

## Consensus Networks as Agreement Mechanism for Autonomous Agents in Water Markets

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Es el título de nuestro paper en las Jornadas que organiza el $latex im^2$ (Instituto de Matemática Multidisciplinar) de la UPV: Mathematical Models for Addictive Behaviour, Medicine & Engineering. El tema es el uso de redes de consenso para alcanzar acuerdos de forma descentralizada, aplicado en concreto a problemas de gestión de recursos hídricos. A continuación te dejo el resumen (en inglés) y las trasparencias de la presentación. En cuanto esté publicado dejaré también la referencia completa al artículo y, si puedo por temas de licencia, el enlace.

Abstract

The aim of this paper is to present a way of share opinions in a decentralized way by a set of agents that try to achieve an agreement by means of a Consensus Network, allowing them to know beforehand if there is possibilities to achieve such an agreement or not.
The theoretical framework for solving consensus problems in dynamic networks of agents was formally introduced by Olfati-Saber and Murray (2004). The interaction topology of the agents is represented using directed graphs and a consensus means to reach an agreement regarding a certain quantity of interest that depends on the state of all agents in the network. This value represents the variable of interest in our problem.

A consensus network is a dynamic system that evolves in time. Consensus of complete network is reached if and only if $latex x_i = x_j \forall i, j$. Has  been de demonstrated that a convergent and distributed consensus algorithm in discrete-time can be written as follows:

$latex x_i(k+1)=x_i(k) + \varepsilon \sum_{j \in N_i} a_{ij}(x_j(k)-x_i(k))$

where $latex N_i$ denotes the set formed by all nodes connected to the node i (neighbors of i). The collective dynamics of the network for this algorithm can be written as $latex x(k+1)=Px(k)$, where $latex P=I-\varepsilon L$ is the Perron matrix of a graph with parameter $latex \varepsilon$. The algorithm converges to the average (or other functions) of the initial values of the state of each agent and allows computing the average for very large networks via local communication with their neighbors on a graph.
The convergence of this method depends on the topology of the network and its convergence is usually exponential. But sometimes it not needed to reach a final agreement on a concrete value. This proposal uses consensus networks to determine if an agreement is possible among a set of entities. Agents can leave the agreement if its parameters are out of the expected bounds, so the consensus network can be used to detect the candidate agents to be members of the final agreement. All this process is solved in a self-organized way and each individual agent decides to belong or not to the final solution.
To show the validity of the present approach, a water market is presented as case of study. The water market is a case of complex social-ecological system (SES), where centralized and hierarchical approaches trend to fail and self-organized solutions seems to be more sustainable in the long term (Ostrom, 2009). In general, agreements related to natural resource management involve very complex negotiations among agents. Water demands and regulation is a very complex distributed domain appropriated for MAS.
An important question is if this kind of markets requires some regulation or not. From an exclusively economic point of view the dominant strategy for agents in deregulated markets is not cooperative because each agent wants to maximize exclusively his payoff, and therefore they are not interested in the global and socially efficiency of the natural resources.

## Small World for Agent Search

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Es el título de mi póster en el AAMAS '09. Se trata de evaluar si es válido un modelo de red de tipo small world para distribuir a un grupo de plataformas  de agentes en una red de forma que se pueda localizar fácilmente dónde se encuentra un agente con el que nos queremos comunicar.

El modelo de red que se emplea ha sido propuesto por Kleinberg y garantiza que se pouede realizar un proceso de búsqueda voraz (tomando decisiones de forma local y sin volver atrás) acotado. A este tipo de redes se les llama redes navegables.

En un artículo más extenso lo he comparado con otros modelos de redes de tipo small world y la verdad es que sale bastante bien parado: es una red tan buena como la mejor (el modelo de Barabasi según mis pruebas) en cuanto a tolerancia a fallos (destrucción de enlaces en la red), pero mucho mejor en cuanto a la búsqueda, mejorando incluso a los modelos P2P.

Referencia

REBOLLO, M.: Small World Model for Agent Search (Short Paper).- In Proc. of 8th Int. Conf. on Autonomous Agents and Multiagent Systems (AAMAS 2009), Decker, Sichman, Sierra and Castelfranchi (eds.), May, 10–15, 2009, Budapest, Hungarytions.

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