Roberto Centeno

Organising MAS: a formal model based on organisational mechanisms

In this paper, we propose a general formal framework for organising multiagent systems whose participants are rational agents. This model is based on the idea of organisational mechanisms. These are mechanisms introduced in a multiagent system with the aim of influencing the behaviour of the agents towards more effectiveness with regard to some objectives. We define two kinds of organisational mechanisms: i) informative mechanisms which provide additional information to agents, that may persuade agents to behave in a certain way, and ii) regulative mechanisms which produce changes in the environment of the agents, that may impose certain behaviours. We also define some properties of these mechanisms which will make it possible to prove certain characteristics of organised multiagent systems. Finally, we present a discussion about how the social concepts proposed by different organisational paradigms can be considered as either informative or regulative organisational mechanisms.

A Hybrid Reputation Model Based on the Use of Organizations

In this paper we present a hybrid reputation model focused on organizational structures that attempts to solve problems associated with both centralized and decentralized reputation models. Agents in our approach are able not only to evaluate the behavior of others and store reputations values but also to send such information to a centralized mechanism and ask for reputations to this one and to other agents. The main objective of our approach is to allow agents to reason about the reputation values that they receive. Therefore, together with the reputation values, agents store and send information about norms violated and fulfilled and about the facts that contributed to such behavior. Furthermore, this model provides two different types of reputations, as service provider that is related to the behavior of an agent while providing a service to other agents and as reputation source that is related to the behavior of an agent while providing reputation of others.

From blurry numbers to clear preferences: A mechanism to extract reputation in social networks

Complex social networks are typically used in order to represent and structure social relationships that do not follow a predictable pattern of behaviour. Due to their openness and dynamics, these networks make participants continuously deal with uncertainty before any type of interaction. Reputation appears as a key concept helping users to mitigate such uncertainty. Most of the reputation mechanisms proposed in the literature are based on numerical opinions (ratings), and consequently, they are exposed to potential problems such as the subjectivity in the opinions and their consequent inaccurate aggregation. With these problems in mind, this paper presents a reputation mechanism based on the concepts of pairwise elicitation processes and knock-out tournaments. The main objective of this mechanism is to build reputation rankings from qualitative opinions, thereby removing the subjectivity problems associated with the aggregation of quantitative opinions. The proposed approach is evaluated with different data sets from the MovieLens and Flixster web sites.

On the inaccuracy of numerical ratings: dealing with biased opinions in social networks

In this work, we study the potential problems emanating from using numerical ratings in social networks to rank entities regarding their reputation. In particular, we empirically demonstrate how reputation rankings as collected and managed by current systems are likely to be skewed due to subjectivity problems associated with the use of numerical ratings to encapsulate preferences. With the aim of overcoming these problems, we put forward an approach in which users are asked for their opinions about entities in a comparative fashion. In order to select the most appropriate users to be queried, we take advantage of the social structure derived from the interactions among users and entities following a principle of heterogeneity. Finally, we evaluate the proposed approach in the domain of movie ratings by using real datasets collected from different web sites.

An Adaptive Sanctioning Mechanism for Open Multi-agent Systems Regulated by Norms

This work presents an adaptive sanctioning mechanism that can be applied in open multi-agent systems that are regulated through norms. This mechanism tries to identify the attributes of the environment that have some influence on agents decision making and uses such attributes to define sanctions that may prevent norm violations. Our approach adapts sanctions to particular agents and particular environmental states. The mechanism is deployed by using an infrastructure of institutional agents in charge of adapting and applying sanctions to external agents. The proposal is evaluated empirically in a p2p scenario, comparing it with a traditional sanctioning approach for normative systems.

Effective use of organisational abstractions for confidence models

Trust and reputation mechanisms are commonly used to infer expectations of future behaviour from past interactions. They are of particular relevance when agents have to choose appropriate counterparts for their interactions as it may also happen within virtual organisations. However, when agents join an organisation, information about past interactions is usually not available. The use of organisational structures can tackle this problem and can improve the efficiency of trust and reputation mechanisms by endowing agents with some extra information to choose the best agents to interact with. In this context, we present how certain structural properties of virtual organisations can be used to build an efficient trust model in a local way. Furthermore, we introduce a testbed (TOAST) that allows to analyse different trust and reputation models in situations where agents act within virtual organisations. We experimentally evaluate our approach and show its validity.

Supporting Medical Emergencies by MAS

In the emerging field of m-Health, advanced applications provide healthcare to people anywhere, anytime using broadband and wireless communications, as well as mobile computing devices. The notion of Service-Oriented Multi-Agent Systems (SOMAS) that has recently been proposed appears to adequately capture the requirements of applications in this field. The THOMAS abstract architecture and software platform supports the construction of SOMAS around an organisational metaphor. In this paper we present an application prototype built on top of THOMAS for a real-world mHealth scenario: mobile medical emergency management in an urban area.

Using incentive mechanisms for an adaptive regulation of open multi-agent systems

In this paper we propose a mechanism that encourages agents, participating in an open MAS, to follow a desirable behaviour, by introducing modifications in the environment. This mechanism is deployed by using an infrastructure based on institutional agents called incentivators. Each external agent is assigned to an incentivator that is able to discover its preferences, and to learn the suitable modifications in the environment, in order to improve the global utility of a system in response to inadequate design or changes in the population of participating agents. The mechanism is evaluated in a p2p scenario.

Artifacting and Regulating the Environment of a Virtual Organization

This work presents an extension of the Environment Dimension of the Virtual Organization Model, which is an Organization Modeling Language to define Organization-Centered Multi-Agent Systems. This extension allows this model to regulate the environment by supporting artifacts for organizational mechanisms, an approach based on the Agents & Artifacts conceptual framework. The three main entities of this framework are agents, artifacts and workspaces, which have been integrated in this work inside the Virtual Organization Model. Additionally, this paper presents an application to the health care setting and an analysis of the related work on this topic.

ENHANCING MAS ENVIRONMENTS WITH ORGANIZATIONAL MECHANISMS

Organizational mechanisms can be introduced in a multi-agent system with the aim of influencing the behavior of agents to achieve their objectives in a proper way. Thus, they are designed to achieve a better coordination between agents. In this paper, we propose to model organizational mechanisms by means of artifacts, which were presented within the Agents & Artifacts approach, and that present good advantages for coordinating agents environments. We claim that artifacts, as reactive entities located into the environment of a Multi-agent System, can help agents to reach their goals, seem to be a suitable abstraction for modeling organizational mechanisms. We also give some examples of possible uses.