From the very early days of the World Wide Web, researchers identified a need to be able to understand the semantics of the information on the Web in order to enable intelligent systems to do a better job of processing the booming Web of documents. Early proposals included labeling different kinds of links to differentiate, for example, pages describing people from those describing projects, events, and so on. By the late 90’s, this effort had led to a broad area of Computer Science research that became known as the Semantic Web [Berners-Lee et al. 2001]. In the past decade and a half, the early promise of enabling software agents on the Web to talk to one another in a meaningful way inspired advances in a multitude of areas: defining languages and standards to describe and query the semantics of resources on the Web, developing tractable and efficient ways to reason with these representations and to query them efficiently, understanding patterns in describing knowledge, and defining ontologies that describe Web data to allow greater interoperability.