Structure of This Book

The first section of this book (Chapter 1 through Chapter 6) focuses on the RDF specifications. Chapter 1 focuses on introducing RDF, but more than that, it also looks at some of the historical events leading up to the current RDF effort. In addition, this chapter also looks at issues of when you would, and would not, use RDF/XML as compared to "standard" XML.

Following the introductory chapter, the rest of the first section covers the RDF specification documents themselves. This includes coverage of the RDF Semantics and Concepts and Abstract Model specifications (covered in Chapter 2); the basic XML syntax (covered in Chapter 3); coverage of some of the more unusual RDF constructs—containers, collections, and reification (covered in Chapter 4); and the RDF Schema (covered in Chapter 5). As a way of pulling all of the coverage together, Chapter 6 then uses all we've learned about RDF to that point to create a relatively complex vocabulary, which is then used for demonstration purposes throughout the rest of the book.

The second section of the book focuses on programming language support, as well as the tools and utilities that allow a person to review, edit, parse, and generally work with RDF/XML. Chapter 7 focuses on various RDF editors, including those with graphical support for creating RDF models. In addition, the chapter also covers an RDF/XML browser, as well as a couple of the more popular RDF/XML parsers.

To be useful, any specification related to data requires tools to work with the data, and RDF is no exception. Chapter 8 provides an overview and examples of accessing and generating RDF/XML using Jena, a Java-based RDF API. Chapter 9, which covers APIs that are based in PHP, Perl, and Python—the three Ps—follows this.

After the programming language grounding, the book refocuses on RDF's data roots with a chapter that examines some of the RDF query languages used to query RDF model data, in a database or as persisted to RDF/XML documents. Chapter 10 also has the code for the RDF Query-O-Matic, a utility that processes RDQL (RDF Query Language) queries.

The last chapter in the second section finishes the review of programming and framework support for RDF by looking at some other programming language support, as well as some of the frameworks, such as Redland and Redfoot.

The last section of the book then focuses on the use of RDF and RDF/XML, beginning with an overview of the W3C's ontology language effort, OWL. If RDF is analogous to the relational data model, and RDF/XML is analogous to relational database systems, then OWL is equivalent to applications such as SAP and PeopleSoft, which implement a business domain model on top of the relational store.

The next chapter focuses on RSS, the implementation of RDF/XML most widely used, which supports syndication and aggregation of news sources. RSS is used to syndicate news sources as diverse as salon.com and Wired, as well as online personal journals known as weblogs, a web technology gaining popularity.

A specification is only as good as the applications that use it, and RDF is used in a surprising number of sophisticated commercial and noncommercial applications. I say "surprising" primarily because RDF is not a well-known specification. However, it is one of the older specifications. RDF's maturity, combined with the specification's data manipulation and organizational capabilities, makes it easy to see why the growing interest in RDF is arising.

The RDF Validator-generated graphs have been replaced with illustrations in order to fit the examples within the constraints imposed by the page width.