Science is like a tree: contrary to popular belief, both trees and science grow at their edges, not at their core. For science, this means that most of the fruitful and exciting developments are not happening at the core of established fields, but are instead happening at the boundaries between such fields. This has been particularly true for Computer Science. The most interesting database developments don’t happen inside the Database community, but rather where databases hit Biology. Similarly, the most interesting developments in Ar-—cial Intelligence in recent years have happened where AI met the Web. The young field of Semantic Web research has been one of the results of a number of different subfields of Computer Science being exposed to the challenges of the Web: databases, computational linguistics, knowledge representation, knowled- based systems and service-oriented computing are just some of the subfields that are all making contributions to the Semantic Web vision, namely a Web that consists not only of linksbetween web-pagesfull of picturesand text, but of a Semantic Web that consists of links between computer-interpretable data. Such a Semantic Web would make it possible to query and reason over integrated data-sets consisting of separate pieces of information that were never intended to be linked together, but that can nevertheless be fruitfully combined and integrated, sometimes even by a third party who neither wrote nor ownsany of the original piecesof data (just as is possible with web-pages on the current Web).