Friday, May 06, 2005

Where are the Semantics in the Semantic Web? 

Where are the Semantics in the Semantic Web?
"ABSTRACT
The most widely accepted defining feature of the Semantic Web is machine-usable content. By this definition, the Semantic Web is already manifest in shopping agents that automatically access and use Web content to find the lowest air fares, or book prices. But where are the semantics? Most people regard the Semantic Web as a vision, not a reality—so shopping agents should not “count”. To use Web content, machines need to know what to do when they encounter it. This in turn, requires the machine to “know” what the content means (i.e. its semantics). The challenge of developing the Semantic Web is how to put this knowledge into the machine. The manner in which this is done is at the heart of the confusion about the Semantic Web. The goal of this paper is to clear up some of this confusion.
We proceed by describing a variety of meanings of the term “semantics”, noting various things that can be said to have semantics of various kinds. We introduce a semantic continuum ranging from implicit semantics, which are only in the heads of the people who use the terms, to formal semantics for machine processing. We list some core requirements for enabling machines to use Web content, and we consider various issues such as hardwiring, agreements, clarity of semantics specifications, and public declarations of semantics. In light of these requirements and issues in conjunction with our semantic continuum, it is useful to collectively regard shopping agents as a degenerate case of the Semantic Web. Shopping agents work in the complete absence of any explicit account of the semantics of Web content because the meaning of the Web content that the agents are expected to encounter can be determined by the human programmers who hardwire it into the Web application software.
We note various shortcomings of this approach, which give rise to some ideas about how the Semantic Web should evolve. We argue that this evolution will take place by (1) moving along the semantic continuum from implicit semantics to formal semantics for machine processing, (2) reducing the amount of Web content semantics that is hardwired, (3) increasing the amount of agreements and standards, and (4) developing semantic mapping and translation capabilities where differences remain."

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