IEEE DISTRIBUTED SYSTEMS ONLINE 1541-4922 © 2004 Published by the IEEE Computer Society Vol. 5, No. 8; August 2004

An Introduction to RDF Technologies: Too Little, Too Soon

Minor Gordon

Practical RDFBy Shelley Powers 331 pages US$39.95 O'Reilly, 2003 ISBN 0-596-00263-7

The Resource Description Framework is to the emerging Semantic Web what HTML is to the current World Wide Web. The Semantic Web is not a new Web, but an extension of the current one; likewise, RDF is not a new HTML, but a framework for making logical assertions about resources on the Web, including existing HTML Web pages. The "semantics" are in the connections between assertions, which form a Semantic Web.

Practical RDF is a feet-first leap into the theory and applications of RDF and other Semantic Web technologies and software. It's one of the first books to attempt to survey the fast-changing world of Semantic Web development. There's a reason other publishers have held back: most of the book's material was out of date before the text was even printed. RDF and the Web Ontology Language (OWL) didn't become World Wide Web Consortium (W3C) Recommendations until February 2004, and only after much discussion and evolution of the specifications. Shelley

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Powers's dated text reflects these transitions; it's littered with disclaimers about outdated software and document versions. One is left wondering why O'Reilly published the book at all. Given the ephemeral subject matter, the text would have been more useful as an extended Web tutorial.

Ironically, Practical RDF reads like a set of Web pages; the reader is meant to take information from it as needed, rather than reading it straight through. The book includes introductory chapters on RDF, OWL, and other basic Semantic Web technologies, as well as pointers to current Web resources. However, the necessarily simplified treatment of a very complex topic (RDF's graph theoretic foundations are the products of over a century's worth of philosophical, mathematical, and artificial intelligence research) would probably confuse a novice.

Rather than serving as an introduction, however, the book concentrates on "using RDF and the associated RDF/XML in our day-to-day technology projects." Powers briefly describes RDF's theoretical basis before delving into the details of RDF/XML serialization. After explaining how to create validatable RDF vocabularies with RDF Schema, she surveys an array of software tools for manipulating RDF. These include programming APIs in Java (Jena) and other languages, as well as more user-centric applications such as the IsaViz editor. Chapter 10 surveys the state of the art in querying RDF data sources using Structured Query Language (SQL)-derived languages such as Resource Description Query Language (RDQL). A more in-depth look into OWL follows. The book's final sections consider existing applications of RDF, such as RSS (RDF Site Summary) and FOAF (Friend of a Friend), among others.

Although Powers tries to position RDF as a tool for "business applications today, rather than in some Semantic Web some day," the book ends up reflecting (and reproducing) many of the Semantic Web effort's shortcomings especially its immaturity. Unlike other W3C specifications such as SOAP and XML, RDF has yet to find a definite place in the commercial world. The framework is still a toy for academics and amateurs, and neither of these groups needs a book like Practical RDF. Anyone seriously interested in learning about and using Semantic Web technologies should refer to original sources, such as the W3C's RDF Primer or the Jena tutorial; in fact, the most lucid parts of Practical RDF are the ones Powers reproduced most faithfully from these sources.

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Powers's commentary, asides, and extraneous details don't add much value to the material, either. Even worse, some of her statements (and numerous restatements) only confuse an otherwise simple idea. An example from page 8: " RDF provides a structure that allows us to make assertions using XML (and other serialization techniques)." Although this statement isn't technically false, it confuses the role of XML in RDF at an early point in the text when a beginning reader might be easily misled. To add to the confusion, Powers goes on to state that " there is an interest in taking this further and expanding on it, by creating just such an ontology based on the RDF model, in the interest of supporting more advanced agent-based technologies." This sounds like the first sentence of a conference paper, instead of the introduction to an O'Reilly text.

Conclusion

In spite of its laudable publisher, Practical RDF is rife with foibles. The book's one saving grace might be the plethora of links scattered throughout the text; these could lead readers back to source pages that are actually worth reading.

Minor Gordon is a graduate student at the Technische Universität Berlin. Contact him at minorg@cs.okstate.edu.

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