ABSTRACT
The Resource Description Framework RDF is a formal language for describing structured information. The goal of RDF is to enable applications to exchange data on the Web while still preserving their original meaning. As opposed to HTML and XML, the main intention now is not to display documents correctly, but rather to allow for further processing and re-combination of the information contained in them. RDF consequently is often viewed as the basic representation format for developing the Semantic Web. The development of RDF began in the 1990s, and various predecessor lan-
guages have influenced the creation process of RDF. A first official specification was published in 1999 by the W3C, though the emphasis at this time still was clearly on the representation of metadata about Web resources. The term metadata generally refers to data providing information about given data sets or documents. In 1999, the latter were mainly expected to be Web pages, for which RDF could help to state information on authorship or copyright. Later the vision of the Semantic Web was extended to the representation of semantic information in general, reaching beyond simple RDF data as well as Web documents as primary subjects of such descriptions. This was the motivation for publishing a reworked and extended RDF specification in 2004. As of today, numerous practical tools are available for dealing with RDF.
Virtually every programming language offers libraries for reading and writing RDF documents. Various RDF stores – also called triple stores for reasons that shall become clear soon – are available for keeping and processing large amounts of RDF data, and even commercial database vendors are already providing suitable extensions for their products. RDF is also used to exchange (meta) data in specific application areas. The most prominent example of this kind of usage is likely to be RSS 1.0 for syndicating news on the Web.1 But also metadata belonging to files of desktop applications are sometimes encoded using RDF, such as in the case of Adobe’s RDF format XMP for embedding information in PDF files, or as annotations in the XML-based vector graphics format SVG. We will say more about such applications in Chapter 9.
