Annotation. This book constitutes the refereed proceedings of the 4th InternationalConference on Web Reasoning and Rule Systems, RR 2010, held inBrixen-Bressanone, Italy, in September 2010. The 9 revised full papers, 6 revised short papers, and 4 poster paperspresented together with 1 PhD paper, 2 system descriptions and 3 invitedpapers were carefully reviewed and selected from 41 submissions. Thepapers address all current topics in Web reasoning, Web-based knowledge, and rule systems such as representation techniques; rules andontologies; reasoning languages; efficiency and benchmarking, ; ontologylanguages; querying and optimization; reasoning with uncertainty, underinconsistency, and with constraints; rule languages and systems; ruleinterchange formats and markup languages; scalability; approximatereasoning; statistical methods and symbolic reasoning; as well assemantic Web services modeling and applications.

Answer Set Programming (ASP) is a declarative problem solving approach, initially tailored to modeling problems in the area of Knowledge Representation and Reasoning (KRR). More recently, its attractive combination of a rich yet simple modeling language with high-performance solving capacities has sparked interest in many other areas even beyond KRR. This book presents a practical introduction to ASP, aiming at using ASP languages and systems for solving application problems. Starting from the essential formal foundations, it introduces ASP's solving technology, modeling language and methodology, while illustrating the overall solving process by practical examples. Table of Contents: List of Figures / List of Tables / Motivation / Introduction / Basic modeling / Grounding / Characterizations / Solving / Systems / Advanced modeling / Conclusions