Constitutes the refereed proceedings of the 4th International Symposium on Foundations of Information and Knowledge Systems, held in February 2006. This book covers such topics as: the theoretical foundations of information and knowledge systems, as well as mathematical fields such as discrete mathematics and combinatorics.

Invited Presentation.- The Semijoin Algebra.- Regular Papers.- Equational Constraint Solving Via a Restricted Form of Universal Quantification.- Modeling the Evolution of Objects in Temporal Information Systems.- Controlled Query Evaluation with Open Queries for a Decidable Relational Submodel.- Iterative Modification and Incremental Evaluation of Preference Queries.- On the Number of Independent Functional Dependencies.- Arity and Alternation: A Proper Hierarchy in Higher Order Logics.- Solving Abduction by Computing Joint Explanations: Logic Programming Formalization, Applications to P2P Data Integration, and Complexity Results.- The Nested List Normal Form for Functional and Multivalued Dependencies.- Axiomatising Functional Dependencies for XML with Frequencies.- Guarded Open Answer Set Programming with Generalized Literals.- Reasoning Support for Expressive Ontology Languages Using a Theorem Prover.- Consistency Checking Algorithms for Restricted UML Class Diagrams.- Some Contributions to the Minimum Representation Problem of Key Systems.- On Multivalued Dependencies in Fixed and Undetermined Universes.- Preference-Based Query Tuning Through Refinement/Enlargement in a Formal Context.- Processing Ranked Queries with the Minimum Space.- Hybrid Minimal Spanning Tree and Mixture of Gaussians Based Clustering Algorithm.

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