This article first reminds of simulation unification, a non-standard unification proposed at the 18th International Conference on Logic Programming (ICLP 2002) for making logic programming capable of querying semistructured data on the Web. This article further argues that, beyond querying semistructured data on the Web, simulation unification has a potential for Web querying of multimedia data and semantic metadata and for Web searching of data of all kinds.

Abstract—The publication of Linked Open Data on the Web has gained tremendous momentum over the last six years. As a consequence, we currently witness the emergence of a new research area that focuses on an online execution of Linked Data queries; i.e., declarative queries that range over Web data that is made available using the Linked Data publishing principles. These principles only require Web servers that respond to sim-ple requests for data about given entities. Therefore, in contrast to approaches for querying a more traditional distributed database, Linked Data query processing approaches cannot assume that data sources provide query processing functionality. Additional challenges are the unbounded nature of the Web and the lack of a complete, up-to-date database catalog that lists all data sources. Our tutorial provides an overview of the new area of Linked Data query processing. We introduce the foundations of Linked Data queries, discuss the specific challenges that need to be addressed, and review techniques for executing such queries. I.