Semantic Web Programming

Appendix A. RDF

This appendix describes the Resource Description Framework (RDF), an important technology for information representation that underlies many of the concepts and tools that are described in the book. This appendix is intended to serve as a concise refresher for the main RDF concepts and as a reference for the syntax and general usage for the most commonly used constructions in the book. RDF and the broader Semantic Web knowledge model are described in much more depth in Chapter 3, "Modeling Information."

Basic RDF takes a generalized graph-based approach to representing information so that it can be easily shared and mixed together. Like the notion of a graph itself, RDF is not a language per se but is an abstract information model that can be serialized in multiple ways. RDF represents information as a graph of related statements. A statement is made up of three elements, a subject, a predicate, and an object. In the graph, a statement represents a directed edge between two nodes, with the predicate (also referred to as a property) representing the edge, and the subject and object representing nodes. RDF defines two basic types of nodes: literals and resources. A literal is a concrete value, such as a string or a number, and literals cannot be the subjects of statements, only the objects. Resources represent, generally speaking, anything that can be assigned an International Resource Identifier (IRI). Examples of resources include people, things, locations, and concepts. ...