As stated earlier, the RDF specification was originally released as one document, the RDF Model and Syntax, or RDF M&S. However, it soon became apparent that this document was attempting to cover too much material in one document, and leaving too much confusion and too many questions in its wake. Thus, a new effort was started to address the issues about the original specification and, hopefully, eliminate the confusion. This work resulted in an updated specification and the release of six new documents: RDF Concepts and Abstract Syntax, RDF Semantics, RDF/XML Syntax Specification (revised), RDF Vocabulary Description Language 1.0: RDF Schema, the RDF Primer, and the RDF Test Cases.
The RDF Concepts and Abstract Syntax and the RDF Semantics documents provide the fundamental framework behind RDF: the underlying assumptions and structures that makes RDF unique from other metadata models (such as the relational data model). These documents provide both validity and consistency to RDF?a way of verifying that data structured in a certain way will always be compatible with other data using the same structures. The RDF model exists independently of any representation of RDF, including RDF/XML.
The RDF/XML syntax, described in the RDF/XML Syntax Specification (revised), is the recommended serialization technique for RDF. Though several tools and APIs can also work with N-Triples (described in Chapter 2) or N3 notation (described in Chapter 3), most implementation of and discussion about RDF, including this book, focus on RDF/XML
The RDF Vocabulary Description Language defines and constrains an RDF/XML vocabulary. It isn't a replacement for XML Schema or the use of DTDs; rather, it's used to define specific RDF vocabularies; to specify how the elements of the vocabulary relate to each other. An RDF Schema isn't required for valid RDF (neither is a W3C XML Schema or an XML 1.0 Document Type Definition?DTD), but it does help prevent confusion when people want to share a vocabulary.
A good additional resource to learn more about RDF and RDF/XML is the RDF Primer. In addition to examples and accessible descriptions of the concepts of RDF and RDFS, the primer also, looks at some uses of RDF. I won't be covering the RDF Primer in this book because its use is somewhat self-explanatory. However, the primer is an excellent complement to this book, and I recommend that you spend time with it either while you're reading this book or afterward if you want another viewpoint on the topics covered.
The final RDF specification document, RDF Test Cases, contains a list of issues arising from the original RDF specification release, their resolutions, and the test cases devised for use by RDF implementers to test their implementations against these resolved issues. The primary purpose of the RDF Test Cases is to provide examples for testing specific RDF issues as the Working Group resolved them. Unless you're writing an RDF/XML parser or something similar, you probably won't need to spend much time with that document, and I won't be covering it in the book.