RDF's purpose is fairly straightforward: it provides a means of recording data in a machine-understandable format, allowing for more efficient and sophisticated data interchange, searching, cataloging, navigation, classification, and so on. It forms the cornerstone of the W3C effort to create the Semantic Web, but its use isn't restricted to this specific effort.
Perhaps because RDF is a description for a data model rather than a description of a specific data vocabulary, or perhaps because it has a foothold in English, logic, and even in human reasoning, RDF has a strong esoteric element to it that can be intimidating to a person wanting to know a little more about it. However, RDF is based on a well-defined set of rules and constraints that governs its format, validity, and use. Approaching RDF through the specifications is a way of grounding RDF, putting boundaries around the more theoretical concepts.
The chapter takes a look at two RDF specification documents that exist at opposite ends of the semantic spectrum: the RDF Concepts and Abstract Model and the RDF Semantics documents. In these documents we're introduced to the concepts and underlying strategy that form the basis of the RDF/XML that we'll focus on in the rest of the book. In addition, specifically within the Semantics document, we'll be exposed to the underlying meaning behind each RDF construct. Though not critical to most people's use of RDF, especially RDF/XML, the Semantics document ensures that all RDF consumers work from the same basic understanding; therefore, some time spent on this document, primarily in overview, is essential.
Both documents can be accessed directly online, so I'm not going to duplicate the information contained in them in this chapter. Instead, we'll take a look at some of the key elements and unique concepts associated with RDF.