This book constitutes the refereed proceedings of the 4th European Semantic Web Conference, ESWC 2007, held in Innsbruck, Austria, in June 2007. Coverage includes semantic Web services, ontology learning, inference and mapping, social semantic Web, ontologies, personalization, foundations of the semantic Web, natural languages and ontologies, and querying and Web data models.

Here are the proceedings of the 4th International Workshop on Principles and Practice of Semantic Web Reasoning, PPSWR 2006. The book presents 14 revised full papers together with 1 invited talk and 6 system demonstrations, addressing major aspects of semantic Web research, namely forms of reasoning with a strong interest in rule-based languages and methods. Coverage includes theoretical work on reasoning methods, concrete reasoning methods and query languages, and practical applications.