Robert Brandom has provided what is probably one of the best worked out accounts of how the meanings of linguistic expressions are determined by how they are used—in particular, used in inferences. There are three different types of inferential relations in terms of which Brandom gives his account: commitment-preserving, entitlement-preserving, and incompatibility relations. Brandom also recognizes that most of the reasoning we engage in is defeasible (or deductively inconclusive). For example, the inference from ‘Tweety is a bird’ to ‘Tweety can fly’ is defeasible, because it can be defeated if there is stronger overriding reason to deny that ‘Tweety can fly’—such as Tweety’s being a penguin. Surprisingly, Brandom’s three types of inferential relations are inadequate for describing defeasible inference. In my dissertation I explain how the problem arises—it’s actually two problems—and I propose a solution that is consistent with Brandom’s overall approach. The first problem is that although Brandom's account does explain how someone can lose entitlement to a claim by committing themselves to some other claim, as in the Tweety example, it doesn’t allow subsequent recovery of entitlement to that claim by the addition of yet further information—say, that Tweety is a penguin with a jetpack. Once defeated (by some information), an inference stays defeated, on Brandom's account. The second problem is that of interpretation: when should we interpret someone as committed to the propriety of an inference that is defeasible? Brandom's account of what it is to endorse an inferential relation has no room for the important distinction between endorsing an inference in a context in which it happens to be defeated, and not endorsing it at all. In the latter portion of this dissertation I propose various modifications to Brandom’s account that will allow it overcome these problems. I solve the first problem by modifying Brandom’s account of how someone is obliged to update their beliefs in light of the inferential relations they endorse. I solve the second problem by modifying Brandom’s account of when we can appropriately interpret someone as endorsing particular inferential relations.

Purchasing products from online e-stores is getting popular with the advance of Internet infrastructure and network security. At current stage, most e-stores resemble vending machines rather than real stores because they lack clerks to persuade prospects into buying products and to bargain with the customers for making a good deal. This research aims to design an easy-to-use and autonomous sales-agent, called Isa, to act as a virtual clerk in an e-store. A new approach is proposed to enable the agent to dynamically adopt different persuasion and negotiation strategies according to different characteristics of human buyers. Additionally, this approach enables a sales-agent to learn the best strategies without seller¡¦s instructions. Both laboratory and field experiments are conducted to assess Isa¡¦s performance. The experimental results reveal that Isa can improve a seller¡¦s surplus and increase a buyer¡¦s product evaluation, willingness to pay more money for the product, and satisfaction with visiting the s-store.

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La représentation des connaissances et le raisonnement sur le Web sémantique se sont récemment concentrés, pour des raisons pratiques, sur le sous-ensemble de la logique du premier ordre appelé règles existentielles. Dans cette thèse, nous étudions le raisonnement avec des règles existentielles en présence d'informations contradictoires et introduisons un raisonnement existentiel défaisible. Nous proposons trois résultats principaux: Premièrement, nous montrons que les techniques de raisonnement défaisibles classiques doivent être revisitées pour les règles existentielles et étudions leurs défis théoriques et de mise en œuvre. Deuxièmement, nous fournissons une nouvelle structure combinatoire qui permet de capturer diverses variantes du raisonnement défaisable et étudions son expressivité et sa polyvalence. Troisièmement, nous évaluons notre travail par rapport à l'état de l'art dans le traitement des incohérences et des inconsistances dans les règles existentielles et étudions l'intérêt humain de telles techniques de raisonnement. / Knowledge representation and reasoning on the Semantic Web has recently focused, due to practical rationale, on the subset of first order logic called existential rules. In this thesis we investigate reasoning with existential rules in presence of conflicting information and introduce defeasible existential rule reasoning. We provide three main salient results as follows. First we show that classical defeasible reasoning techniques need to be revisited for existential rules and study their theoretical and implementation related challenges. Second, we provide a new combinatorial structure that allows for diverse variants of defeasible reasoning to be captured together and study its expressivity and versatility. Third we evaluate our work with respect to the state of the art in inconsistency handling in existential rules and investigate the human appeal of such reasoning techniques.

Ensuring privacy and confidentiality concerns of data owners is an important aspect of a secured information system. This is particularly important for integrated systems, which allow data exchange across organizations. Governments, regulatory bodies and organizations provide legislations, regulations and guidelines for information privacy and security to ensure proper data handling. These are usually specified in natural language formats, contain default requirements and exceptions, and are often ambiguous. In addition, interacting concerns, which are often multilayered and from different stakeholders, e.g., jurisdictions, need to be considered in software development. Similar to other security concerns, analysis of confidentiality concerns should be integrated into the early phase of software development in order to facilitate early identification of defects - incompleteness and inconsistencies, in the requirements. This dissertation presents research conducted to develop a method to detect these defects using goal models which support defaults and exceptions. The goal models are derived from annotations of the natural language sources. A prototype tool is also developed to support the method. The evaluations conducted indicate the method and tool provide benefits, including distinguishing requirement interferences and conflicts, exception handling, and navigation between annotated documents and the goal models. Although current limitations of the method include a manual user driven annotation step, the method provides features that assist in early analysis of confidentiality requirements from natural language sources.