Session 1. Invited Talk -- The RuleML Family of Web Rule Languages -- Session 2. Reasoning I -- Automated Reasoning Support for First-Order Ontologies -- Combining Safe Rules and Ontologies by Interfacing of Reasoners -- Session 3. Applications -- Realizing Business Processes with ECA Rules: Benefits, Challenges, Limits -- Interaction Protocols and Capabilities: A Preliminary Report -- Semantic Web Reasoning for Analyzing Gene Expression Profiles -- Session 4. Querying -- Data Model and Query Constructs for Versatile Web Query Languages: State-of-the-Art and Challenges for Xcerpt -- AMa ? oS—Abstract Machine for Xcerpt: Architecture and Principles -- Towards More Precise Typing Rules for Xcerpt -- Session 5. Reasoning II -- Extending an OWL Web Node with Reactive Behavior -- Supporting Open and Closed World Reasoning on the Web -- Reasoning with Temporal Constraints in RDF -- Session 6. Reasoning III -- Bidirectional Mapping Between OWL DL and Attempto Controlled English -- XML Querying Using Ontological Information -- Semantic Web Reasoning Using a Blackboard System -- Systems Session -- Effective and Efficient Data Access in the Versatile Web Query Language Xcerpt -- Web Queries with Style: Rendering Xcerpt Programs with CSSNG -- Information Gathering in a Dynamic World -- Practice of Inductive Reasoning on the Semantic Web: A System for Semantic Web Mining -- Fuzzy Time Intervals System Description of the FuTI–Library -- A Prototype of a Descriptive Type System for Xcerpt.

This book constitutes the refereed proceedings of the 4th International Workshop on Principles and Practice of Semantic Web Reasoning, PPSWR 2006, held in Budva, Montenegro in June 2006 as a satellite event of the 3rd Annual European Semantic Web Conference, ESWC 2006. The 14 revised full papers presented together with 1 invited talk and 6 system demonstrations were carefully reviewed and selected from 25 submissions. The major aspects of semantic Web research are addressed in the papers, namely various forms of reasoning with a strong interest in rule-based languages and methods - ranging from more theoretical work on reasoning methods that can be applied to the semantic Web, concrete reasoning methods and query languages for the semantic Web, to practical applications.