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This volume contains the articles presented at the 6th International Symposium on Foundationsof Informationand KnowledgeSystems (FoIKS 2010)which was held in So?a, Bulgaria during February 15 19, 2010. The FoIKS symposia provide a biennial forum for presenting and discussing theoreticalandappliedresearchoninformationandknowledgesystems.Thegoal is to bring together researchers with an interest in this subject, share research experiences, promote collaboration and identify new issues and directions for future research. FoIKS 2010 solicited original contributions dealing with any foundational aspects of information and knowledge systems. This included submissions that apply ideas, theories or methods from speci?c disciplines to information and knowledge systems. Examples of such disciplines are discrete mathematics, logic and algebra, model theory, information theory, complexity theory, algorithmics and computation, statistics, and optimization. Previous FoIKS symposia were held in Pisa (Italy) in 2008, Budapest (Hungary) in 2006, Vienna (Austria) in 2004, Schloss Salzau near Kiel (Germany) in 2002,and Burg/Spreewaldnear Berlin (Germany) in 2000.FoIKS took up the tradition of the conference series Mathematical Fundamentals of Database Systems (MFDBS), which initiated East West collaboration in the ?eld of database theory. Former MFDBS conferences were held in Rostock (Germany) in 1991, Visegrad (Hungary) in 1989, and Dresden (Germany) in 1987. The FoIKS symposia are a forum for intense discussions. Speakers are given su?cient time to present their ideas and results within the larger context of their research. Furthermore, participants are asked in advance to prepare a ?rst response to a contribution of another author.

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Invited Talks.- Tools and Techniques in Qualitative Reasoning about Space.- A Simple but Formal Semantics for XML Manipulation Languages.- Algorithmic Definability and Completeness in Modal Logic.- Regular Articles.- A Probabilistic Temporal Logic That Can Model Reasoning about Evidence.- An Algorithm for Generating Nash Stable Coalition Structures in Hedonic Games.- Conjunctive Queries with Constraints: Homomorphism, Containment and Rewriting.- Enhancing Dung´s Preferred Semantics.- On the Distance of Databases.- On the Existence of Armstrong Data Trees for XML Functional Dependencies.- Polymorphism in Datalog and Inheritance in a Metamodel.- Possibilistic Semantics for Logic Programs with Ordered Disjunction.- Semantic Web Search Based on Ontological Conjunctive Queries.- Semantically Characterizing Collaborative Behavior in an Abstract Dialogue Framework.- The Relationship of the Logic of Big-Stepped Probabilities to Standard Probabilistic Logics.- Theoretical Foundations for Enabling a Web of Knowledge.- Towards Controlled Query Evaluation for Incomplete First-Order Databases.- Bagging Decision Trees on Data Sets with Classification Noise.- Evolving Schemas for Streaming XML.- ONTO-EVO A L an Ontology Evolution Approach Guided by Pattern Modeling and Quality Evaluation.- Towards a Paradoxical Description Logic for the Semantic Web.- Towards a Unified Model of Preference-Based Argumentation.- Two Complementary Classification Methods for Designing a Concept Lattice from Interval Data.

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