1.1 The Semantic Web and RDF: A Brief History

RDF is based within the Semantic Web effort. According to the W3C (World Wide Web Consortium) Semantic Web Activity Statement:

The Resource Description Framework (RDF) is a language designed to support the Semantic Web, in much the same way that HTML is the language that helped initiate the original Web. RDF is a framework for supporting resource description, or metadata (data about data), for the Web. RDF provides common structures that can be used for interoperable XML data exchange.

Though not as well known as other specifications from the W3C, RDF is actually one of the older specifications, with the first working draft produced in 1997. The earliest editors, Ora Lassila and Ralph Swick, established the foundation on which RDF rested—a mechanism for working with metadata that promotes the interchange of data between automated processes. Regardless of the transformations RDF has undergone and its continuing maturing process, this statement forms its immutable purpose and focal point.

In 1999, the first recommended RDF specification, the RDF Model and Syntax Specification (usually abbreviated as RDF M&S), again coauthored by Ora Lassila and Ralph Swick, was released. A candidate recommendation for the RDF Schema Specification, coedited by Dan Brickley and R.V. Guha, followed in 2000. In order to open up a previously closed specification process, the W3C also created the RDF Interest Group, providing a view into the RDF specification process for interested people who were not a part of the RDF Core Working Group.

As efforts proceeded on the RDF specification, discussions continued about the concepts behind the Semantic Web. At the time, the main difference between the existing Web and the newer, smarter Web is that rather than a large amount of disorganized and not easily accessible data, something such as RDF would allow organization of data into knowledge statements—assertions about resources accessible on the Web. From a Scientific American article published May 2001, Tim Berners-Lee wrote:

The Semantic Web will bring structure to the meaningful content of Web pages, creating an environment where software agents roaming from page to page can readily carry out sophisticated tasks for users. Such an agent coming to the clinic's Web page will know not just that the page has keywords such as "treatment, medicine, physical, therapy" (as might be encoded today) but also that Dr. Hartman works at this clinic on Mondays, Wednesdays and Fridays and that the script takes a date range in yyyy-mm-dd format and returns appointment times.

As complex as the Semantic Web sounds, this statement of Berners-Lee provides the key to understanding the Web of the future. With the Semantic Web, not only can we find data about a subject, we can also infer additional material not available through straight keyword search. For instance, RDF gives us the ability to discover that there is an article about the Giant Squid at one of my web sites, and that the article was written on a certain date by a certain person, that it is associated with three other articles in a series, and that the general theme associated with the article is the Giant Squid's earliest roots in mythology. Additional material that can be derived is that the article is still "relevant" (meaning that the data contained in the article hasn't become dated) and still active (still accessible from the Web). All of this information is easily produced and consumed through the benefits of RDF without having to rely on any extraordinary computational power.

However, for all of its possibilities, it wasn't long after the release of the RDF specifications that concerns arose about ambiguity with certain constructs within the document. For instance, there was considerable discussion in the RDF Internet Group about containers—are separate semantic and syntactic constructs really needed?—as well as other elements within RDF/XML. To meet this growing number of concerns, an RDF Issue Tracking document was started in 2000 to monitor issues with RDF. This was followed in 2001 with the creation of a new RDF Core Working Group, chartered to complete the RDF Schema (RDFS) recommendation as well as address the issues with the first specifications.

The RDF Core Working Group's scope has grown a bit since its beginnings. According to the Working Group's charter, they must now:

• Update and maintain the RDF Issue Tracking document

• Publish a set of machine-processable test cases corresponding to technical issues addressed by the WG

• Update the errata and status pages for the RDF specifications

• Update the RDF Model and Syntax Specification (as one, two, or more documents) clarifying the model and fixing issues with the syntax

• Complete work on the RDF Schema 1.0 Specification

• Provide an account of the relationship between RDF and the XML family of technologies

• Maintain backward compatibility with existing implementations of RDF/XML

The WG was originally scheduled to close down early in 2002, but, as with all larger projects, the work slid until later in 2002. This book finished just as the WG issued the W3C Last Call drafts for all six of the RDF specification documents, early in 2003.