So he went down to the agora, or marketplace, where there were a lot of unemployed
philosophers—which means philosophers which were not thinking at that time.
Thought—in other words, philosophers can tell you millions of things that
thought isn’t, and they can’t tell you what it is—and this bugs them!

—Severn Darden, Lecture on Metaphysics

In the beginning, there was no Web. The Web began as a concept of Tim Berners- Lee, who worked for CERN, the European organization for physics research. CERN’s technical staff urgently needed to share documents located on their many computers. Berners-Lee had previously built several systems to do that, and with this background he conceived the World Wide Web.

The design had a relatively simple technical basis, which helped the technology take hold and gain critical mass. Berners-Lee wanted anyone to be able to put information on a computer and make that information accessible to anyone else, anywhere. He hoped that eventually, machines would also be able to use information on the Web. Ultimately, he thought, this would allow powerful and effective human-computerhuman collaboration:

I have always imagined the information space as something to which everyone has immediate and intuitive access, and not just to browse but to create… Machines become capable of analyzing all the data on the Web—the content, links, and transactions between people and computers.
…when [the Semantic Web] does [emerge], the day-to-day mechanisms of trade, bureaucracy, and our daily lives will be handled by machines talking to machines, leaving people to provide the inspiration and intuition. (Berners- Lee 2000)

I find this vision inspiring, and the means to get there intriguing.

The Semantic Web has, in a way, become almost a celebrity—Scientific American has even published an article on it (Berners-Lee, Hendler, and Lassila 2001)—although most people don’t know what it is, and although there really isn’t a Semantic Web yet. There are many different ideas of what it is, not just one. In this chapter, we examine a range of ideas about what the Semantic Web should be. Some of them may seem futuristic or impractical, but a great deal of work is going on in all the areas we’ll examine.

1.1 What is the Semantic Web?

The word semantic implies meaning or, as WordNet defines it, “of or relating to the study of meaning and changes of meaning.” For the Semantic Web, semantic indicates that the meaning of data on the Web can be discovered—not just by people, but also by computers. In contrast, most meaning on the Web today is inferred by people who read web pages and the labels of hyperlinks, and by other people who write specialized software to work with the data. The phrase the Semantic Web stands for a vision in which computers—software—as well as people can find, read, understand, and use data over the World Wide Web to accomplish useful goals for users.

Of course, we already use software to accomplish things on the Web, but the distinction lies in the words we use. People surf the Web, buy things on web sites, work their way through search pages, read the labels on hyperlinks, and decide
which links to follow. It would be much more efficient and less time-consuming if a person could launch a process that would then proceed on its own, perhaps checking with the person from time to time as the work progressed. The business
of the Semantic Web is to bring such capabilities into widespread use.

In brief, the Semantic Web is supposed to make data located anywhere on the Web accessible and understandable, both to people and to machines. This is more a vision than a technology. In this book, we’ll explore the technologies that will play roles in bringing the vision to life.

As you might expect, there are many different ideas about what this general vision encompasses. An almost overwhelming number of different ideas exists about the supposed nature of the Semantic Web, and that’s the first lesson to
learn: The Semantic Web is a fluid, evolving, informally defined concept rather than an integrated, working system. To give you a feel for this range of ideas, here are some representative quotations about the nature of the Semantic Web:

• The machine-readable-data view - "The Semantic Web is a vision: the idea of having data on the Web defined and linked in a way that it can be used by machines not just for display purposes, but for automation, integration and reuse of data across various applications." (W3C 2003)

• The intelligent agents view - "The aim of the Semantic Web is to make the present Web more machine-readable, in order to allow intelligent agents to retrieve and manipulate pertinent information." (Cost et al 2001)

• The distributed database view - "The Semantic Web concept is to do for data what HTML did for textual information systems: to provide sufficient 4 CHAPTER 1 The Semantic Web flexibility to be able to represent all databases and logic rules to link them together to great added value." (W3C 2000) "A simple description of the Semantic Web is that it is an attempt to do for machine processable data what the World Wide Web did for human readable documents. Namely, to transform information processing by providing a common way that data can be accessed, linked together and understood. To turn the Web from a large hyperlinked book into a large interlinked database." (SWAD-E)

• The automated infrastructure view - "In his recent Scientific American article Berners-Lee argues that the Semantic Web is infrastructure and not an application. We couldn't agree more." (Tuttle et al 2001) "Therefore, the real problem is the lack of an easy automation framework in the current Web." (Garcia and Delgado 2001)

• The servant-of-humanity view - "The vision of the Semantic Web is to let computer software relieve us of much of the burden of locating resources on the Web that are relevant to our needs and extracting, integrating, and indexing the information contained within." (Cranefield 2001) "The Semantic Web is a vision of the next-generation web, which enables web applications to automatically collect web documents from diverse sources, integrate and process information, and interoperate with other applications in order to execute sophisticated tasks for humans." (Anutariya et al 2001)

• The better-annotation view - "The idea of a 'Semantic Web' [Berners-Lee 2001] supplies the (informal) web as we know it with annotations expressed in a machine-processable form and linked together." (Euzenat 2001)

• The improved-searching view - "Soon it will be possible to access Web resources by content rather than just by keywords." (Anutariya et al 2001) "The main goal [of the technology described in the paper] is to build a structured index of the Web site.ˇ± (Desmontils and Jacquin 2001)

• The web services view - "Increasingly, the Semantic Web will be called upon to provide access not just to static documents that collect useful information, but also to services that provide useful behavior." (Klein and Bernstein 2001) "The Semantic Web promises to expand the services for the existing web by enabling software agents to automate procedures currently performed manually and by introducing new applications that are infeasible today." (Tallis, Goldman, and Balzer 2001)

It’s clear that this notion of the Semantic Web covers a lot of ground, and perhaps no two people have quite the same idea about it. Still, several themes are expressed time and again:

• Indexing and retrieving information

• Meta data

• Annotation

• The Web as a large, interoperable database

• Machine retrieval of data

• Web-based services

• Discovery of services

• Intelligent software agents

Let’s look more closely at these themes.