Joana Urbano

"Computational trust modeling is a research field with a fast growing development since the last decade, mainly in the scientific area of distributed artificial intelligence and multi-agent systems, and its potential applicability spreads from social networks to distributed resource sharing and electronic markets. The earliest approaches to computational trust addressed the development of algorithms to aggregate the evidence on any given agent under
evaluation into an estimated score of this agent’s trustworthiness. More recently, the research on computational trust has shifted to the inclusion of third-party information about the trustee under evaluation, including opinions and reputation. However, one important aspect of computational trust has being neglected all these years by the majority of the scholars on computational trust, with a few relevant exceptions: trust is a social construct with a cognitive and an emotional account, and it strongly depends on the relationship existing between the agent that trusts and the one that is trusted.
In this thesis, we address the topic of social trust and its consideration for application in computational trust. We first present a thorough multidisciplinary view of trust, and derive important propositions that will guide our work throughout the thesis. Based on these propositions, we present the SOLUM model, our proposal to computational trust comprised of two distinct parts. The first part is a general framework of computational trust that is based on two fundamental characteristics of trust: trust is more than trustworthiness and other important antecedents to trust, such as the truster’s disposition and emotional state, must be considered when estimation the truster’s trust; and trustworthiness is a multi-dimensional construct that includes the ability, integrity, and benevolence dimensions. This framework can be instantiated and applied to a wide range of trust-based problems and applications, and is seen here as the first main contribution of this thesis. The second part of the SOLUM model includes a set of distinct computational components that (partially) instantiate the framework, namely: Sinalpha, Contextual Fitness, Social Tuner, and Integrity Tuner. We propose the use of specific techniques to extract information about the individual dimensions of the agents’ trustworthiness from the set of structured evidence available on these agents, which may be scarce. This constitutes an innovative view over computational trust, and is the second main contribution of this thesis.
We evaluated our approach through experimental simulation. The results of our experiments allowed us to conclude that it is possible to improve in a relevant way the reliability of the trustworthiness estimations – for the same set of evidence – using the proposed techniques. Consequently, our approach contributes for more informative and secure decisions, in all domains where computer-based trust decisions are needed."

Despite relevant insights from socio-economics, little research in multi-agent systems has addressed the interconnections between trust and normative notions such as contracts and sanctions. Focusing our attention on scenarios of betrayal, in this paper we combine the use of trust and sanctions in a negotiation process.
We describe a scenario of dyadic relationships between truster agents, which make use of trust and/or sanctions, and trustee agents, characterized by their ability and integrity, which may influence their attitude toward betrayal. Both agent behavior models are inspired in socio-economics literature. Through
simulation, we show the virtues and shortcomings of using trust, sanctions, and a combination of both in processes of selection of partners.

Trust estimation is a fundamental process in several multi-agent systems domains, from social networks to electronic business scenarios. However, the majority of current computational trust systems is still too simplistic and is not situation-aware, jeopardizing the accuracy of the predicted trustworthiness values of agents. In this paper, we address the inclusion of context in the trust management process.

Trust and reputation are two distinct social constructs of high complexity that have been studied for decades in different areas of knowledge. In order to allow for efficient models of computational trust and reputation, one must first understand the nature and dynamics of each one of these constructs. In this chapter, we focus on the social and cognitive aspects of the trust concept, and overview its fundamental characteristics, such as its determinants, nature, and dynamics. Then, we present two distinct hypothesis one can state for the interplay between trust and reputation: either reputation is an antecedent of trust, or both are considered as two distinct contributions to the ultimate decision making process. If they are seen as isolated components, trust is no longer directly influenced by reputation. Finally, we briefly refer to current existing computational trust models, including those that integrate the management of computational reputation.

The ANTE framework encompasses results of research efforts on three main agreement technology concepts, namely negotiation, normative environments and computational trust. ANTE has been conceived as a general framework with a wide range of applications in mind. This chapter provides an overview of the main guidelines of this project, and explores two application domains for this framework: automated B2B electronic contracting, and disruption management in the context of an airline company operational control.

Resumo A vulgarização das redes de comunicação de pequena e média dimensão em ambientes Small Office/Home Office (SOHO) tem impulsionado a procura e o desenvolvimento de pequenos dispositivos de fronteira multi-serviço para o acesso à Internet. Uma das componentes de primordial importância destes dispositivos é o subsistema de controlo de tráfego, que permite optimizar a utilização e a distribuição da largura de banda no ponto mais crítico da rede, o acesso à Internet. O trabalho descrito neste artigo insere-se num projecto em desenvolvimento de cooperação entre o Laboratório de Comunicações e Telemática da Universidade de Coimbra e a empresa Critical Software, e que tem como objectivo a construção de um dispositivo de fronteira multi-serviço sobre Linux. Mais concretamente, este artigo aborda os principais problemas encontrados na integração do subsistema de controlo de tráfego com o subsistema de firewall e com gateways de aplicação específicos num mesmo dispositivo Linux – Edge D...

ABSTRACT Previous work on computational trust has delivered robust aggregation engines that proved competent in estimating the trustworthiness of agents. However, most of these approaches were evaluated through simulation using simple and static agents' populations that did not consider the social account of trust. In this paper, we show by experimental analysis that these approaches tend to perform poorly when the populations of agents form social structures that evolve with the situation and the relationship existing between partners. Moreover, we present an approach to social-aware computational trust based on Social Tuner, a new component that we developed that infers the benevolence of the trustee toward the truster from the available evidence. We show by experimental analysis that this approach outperforms the social-less aggregation engines in a relevant way. The experiments are run using a model of agents' behavior grounded on the literature of social trust and benevolence that we have developed and describe in detail in this paper.

Small and medium size networks with access to the Internet are each day more common in SOHO (Small Office/Home Office) environments, comprising domestic and small to medium size organizations. Inherent to the spread of these networks is the search for small access devices that allow the connection to the Internet in a very user friendly way but with a growing number of offered services, comprising basic IP functionalities (eg, DNS, DHCP, SMTP and NAT), security and traffic control services. Traditionally, these services are ...

Resumo Este trabalho insere-se na ��rea das redes de comunica����o de alta velocidade com garantia de qualidade de servi��o (QoS), sendo especialmente focados alguns aspectos importantes nesta ��rea, concretamente, o controlo de congest��o, a reserva de recursos ea especifica����o de requisitos de qualidade de servi��o por parte das aplica����es.

Trust is a construct of paramount importance in society. Accordingly, computational trust is evolving fast in order to allow trust in artificial societies. Despite the advances in this research field, most computational trust approaches evaluate trust by estimating the trustworthiness of the agents under evaluation (the trustees), without however distinguishing between the different dimensions of trustworthiness, such as ability and benevolence. In this paper, we propose different techniques to extract the ability of the trustee in the task at hand and to infer the benevolence of the trustee toward the truster when the trust judgment is made. Moreover, we propose to dynamically change the relative importance and impact of both ability and benevolence on the perceived trustworthiness of the trustee, taking into consideration the development of the relationship between the truster and the trustee and the disposition of the truster in the specific situation. Finally, we set an experimental scenario to evaluate our approach. The results obtained from these experiments show that the proposed techniques significantly improve the reliability of the estimation of the trustworthiness of agents.

Despite relevant insights from socio-economics, little research in multiagent systems has addressed the interconnections between trust and normative notions such as contracts and sanctions. Focusing our attention on scenarios of betrayal, in this paper we combine the use of trust and sanctions in a negotiation process. We describe a scenario of dyadic relationships between truster agents, which make use of trust and/or sanctions, and trustees characterized by their ability and integrity, which may influence their attitude toward betrayal. Both agent behavior models are inspired in socio-economics literature. Through simulation, we show the virtues and shortcomings of exploiting trust, sanctions and a combination of both.

The development of computational trust models is growing in attention in the community of multi-agent systems and these models are currently seen as of extreme importance in social networks, electronic business and grid computing, among others. However, one of the biggest limitations in validating the existing computational trust models is the absence of realistic models of the behavior of agents. In fact, most of the work done in this area assumes that agents behave following simple and static probabilistic models. In this paper, we present a formal model of behavior of business agents that entail in inter-organizational exchanges, taking as basis diverse literature on socio-economic theories. With this model, we empirically show that some of the computational trust approaches which are more cited in the literature are not able to capture the temporal dynamics in the behavior of the business agents. Based on the results obtained from this study, we enumerate different properties that must be present in computational trust models in order to couple with realistic agents’ behavior.

Research on negotiation and task allocation has been in the multi-agent systems realm since its inception as a research field. More recently, social aspects of agent-hood have received increasing attention, namely developing on the fields of normative and trust systems. The integration of these different research contributions will allow to build robust applications for electronic agreement negotiation, aiming at their acceptability and application in industry.

In current days, a great effort, on several scientific research areas, is being devoted to the automation of the procurement processes in the framework of business-to-business relations. However, several constraints limit the extension of the procurement process to truly open and global marketplaces. One such constraint is the lack of valid trust mechanisms that allow business agents to select partners outside the sphere of known relationships, in the hope of better deals.