From iterated revision to iterated contraction: extending the Harper Identity

The study of iterated belief change has principally focused on revision, with the other main operator of AGM belief change theory, namely contraction, receiving comparatively little attention. In this paper we show how principles of iterated revision can be carried over to iterated contraction by generalising a principle known as the ‘Harper Identity’. The Harper Identity provides a recipe for defining the belief set resulting from contraction by a sentence A in terms of (i) the initial belief set and (ii) the belief set resulting from revision by ¬A. Here, we look at ways to similarly define the conditional belief set resulting from contraction by A. After noting that the most straightforward proposal of this kind leads to triviality, we characterise a promising family of alternative suggestions that avoid such a result. One member of that family, which involves the operation of rational closure, is noted to be particularly theoretically fruitful and normatively appealing

Roles '07 – Proceedings of the 2nd Workshop on Roles and Relationships in Object Oriented Programming, Multiagent Systems, and Ontologies : workshop co-located with ECOOP 2007 Berlin, July 30 and 31, 2007

Roles are a truly ubiquitous notion: like classes, objects, and relationships, they pervade the vocabulary of all disciplines that deal with the nature of things and how these things relate to each other. In fact, it seems that roles are so fundamental a notion that they must be granted the status of an ontological primitive. The definition of roles depends on the definition of relationships. With the advent of Object Technology, however, relationships have moved out of the focus of attention, giving way to the more restricted concept of attributes or, more technically, references to other ob- jects. A reference is tied to the object holding it and as such is asymmetric – at most the target of the reference can be associated with a role. This is counter to the intuition that every role should have at least one counter-role, namely the one it interacts with. It seems that the natural role of roles in object-oriented designs can only be restored by installing relationships (collaborations, teams, etc.) as first-class programming concepts. By contrast, the relational nature of roles is already acknowl- edged in the area of Multiagent Systems, since roles are related to the interaction among agents and to communication protocols. However, in this area there is no convergence on a single definition of roles yet, and different points of view, such as agent software en- gineering, specification languages, agent communication, or agent programming languages, make different use of roles. Like its pre- decessor “Roles, an interdisciplinary perspective” (Roles’05) held at the AAAI 2005 Fall Symposium (see the website of the Symposium http://www.aaai.org/Press/Reports/Symposia/Fall/fs-05-08.php), this workshop aimed at gathering researchers from different dis- ciplines to foster interchange of knowledge and ideas concerning roles and relationships, and in particular to converge on ontolog- ically founded proposals which can be applied to programming and agent languages

A conditional perspective of belief revision

Belief Revision is a subarea of Knowledge Representation and Reasoning (KRR) that investigates how to rationally revise an intelligent agent's beliefs in response to new information. There are several approaches to belief revision, but one well-known approach is the AGM model, which is rooted in work by Alchourrón, Gärdenfors, and Makinson. This model provides a set of axioms defining desirable properties of belief revision operators, which manipulate the agent's belief set represented as a set of propositional formulas. A famous extension to the classical AGM framework of Belief Revision is Darwiche and Pearl's approach to iterated belief revision. They uncovered that the key to rational behavior under iteration is adequate preservation of conditional beliefs, i.e., beliefs the agent is willing to accept in light of (hypothetical) new information. Therefore, they introduced belief revision operators modifying the agent's belief state, built from conditional beliefs. Kern-Isberner fully axiomatized a principle of conditional preservation for belief revision, which captures the core of adequate treatment of conditional beliefs during the revision. This powerful axiom provides the necessary conceptual framework for revising belief states with sets of conditionals as input, and it shows that conditional beliefs are subtle but essential for studying the process of belief revision. This thesis provides a conditional perspective of Belief Revision for different belief revision scenarios. In the first part, we introduce and investigate a notion of locality for belief revision operators on the semantic level. Hence, we exploit the unique features of conditionals, which allow us to set up local cases and revise according to these cases, s.t., the complexity of the revision task is reduced significantly. In the second part, we consider the general setting of belief revision with respect to additional meta-information accompanying the input information. We demonstrate the versatility and flexibility of conditionals as input for belief revision operators by reducing the parameterized input to a conditional one for two well-known parameterized belief revision operators who are similarly motivated but very different in their technical execution. Our results show that considering conditional beliefs as input for belief revision operators provides a gateway to new insights into the dynamics of belief revision

Answerers' Motivations and Strategies for Providing Information and Social Support in Social Q&A: An Investigation of Health Question Answering

Social Q&A allows people to ask and answer questions for each other and to solve problems in everyday life collaboratively. The purpose of the current study is to understand the motivations and strategies of answerers in social Q&A. Thus, three research questions were investigated: 1)Why do answerers participate and contribute in social Q&A? 2)What strategies do they use to provide effective answers in social Q&A? 3)What are the relationships between motivations and strategies? The domain of health is chosen because health is one of the most popular topics that people search information and support online. A model of answering behaviors has been proposed with a composition of 10 motivations and 32 strategies related to five steps of answering behaviors - question selection, question interpretation, information seeking, answer creation and answer evaluation. Two research methods - a survey and content analysis - were used. A survey questionnaire was distributed to top answerers and recent answerers in the health category of Yahoo! Answers. Answers of the survey participants were additionally collected in order to analyze the types of health messages and the sources of the answers. Altruism was found to be the most influential motivation, followed closely by Enjoyment and Efficacy. Answerers select questions based on their confidence or interest in the topic of the question. When interpreting questions, answerers believe that they understand the question most of the time. When seeking information for answers, most of the sources of answers are from the answerers' own information and experiences. When creating answers, accuracy and completeness are the most frequently used criteria for evaluating information sources. When evaluating answers, answerers review responses to their answers from questioners, other answerers, and other members in Yahoo! Answers. Additionally, motivations and strategies of all participants, top answerers, and health experts and the relationship between motivations and strategies are reported. Findings from the current study have practical implications for promoting the use of social Q&A as well as other similar Q&A services. The other important research implication is its contributions to the body of knowledge on information providing behaviors