The development of the Semantic Web, with machine-readable content, has the potential to revolutionize the World Wide Web and its use. A Semantic Web Primer provides an introduction and guide to this still emerging field, describing its key ideas, languages, and technologies. Suitable for use as a textbook or for self-study by professionals, it concentrates on undergraduate-level fundamental concepts and techniques that will enable readers to proceed with building applications on their own and includes exercises, project descriptions, and annotated references to relevant online materials. A Semantic Web Primer provides a systematic treatment of the different languages (XML, RDF, OWL, and rules) and technologies (explicit metadata, ontologies, and logic and inference) that are central to Semantic Web development as well as such crucial related topics as ontology engineering and application scenarios. This substantially revised and updated second edition reflects recent developments in the field, covering new application areas and tools. The new material includes a discussion of such topics as SPARQL as the RDF query language; OWL DLP and its interesting practical and theoretical properties; the SWRL language (in the chapter on rules); OWL-S (on which the discussion of Web services is now based). The new final chapter considers the state of the art of the field today, captures ongoing discussions, and outlines the most challenging issues facing the Semantic Web in the future. Supplementary materials, including slides, online versions of many of the code fragments in the book, and links to further reading, can be found at http://www.semanticwebprimer.org.Grigoris Antoniou is Professor at the Institute for Computer Science, FORTH (Foundation for Research and Technology-Hellas), Heraklion, Greece. Frank van Harmelen is Professor in the Department of Artificial Intelligence at the Vrije Universiteit, Amsterdam, the Netherlands.