The Semantic Web

Box of Apples: $5.99

tags. To a human, the meaning is obvious: a box of apples costs $5.99. But a computer can only say that the string of characters "$5.99" follows the string of characters "Box of Apples", or that "of Apples: $5.99" follows "Box ", and so on. This is meaningless. There is no way to ask a computer to find the product (apples) or its cost on a large web page. At best, we can ask it to find a paragraph, but that might not have the information we want. This is why semantic coding has taken on increasing importance in Web 2.0. The more we can describe data using semantic elements, the more that information can be analysed by computers. The importance of this coding method has even led people to begin to envision a Web 3.0, in which all data on the web would be described semantically, opening all of it to computer-based analysis and processing. This is known as the Semantic Web. There is considerable debate about whether such a semantic web is possible (or desirable), but one thing is clear: (X)HTML is not the technology to produce it. Although, as we have seen, (X)HTML has some semantic elements, there are not nearly enough to describe all the possible types of data. A much better technology for Web 3.0 is XML, where the data can have an unlimited number elements and is accompanied by a description of those elements. Nevertheless, the thinking behind the semantic web has ramifications for how we produce web pages. The most important is the principle of separating content from presentation. Wherever possible, content should be represented in (preferably semantic) (X)HTML elements. The presentation, style, or appearance of that content should be conveyed using a different system of markup--normally CSS-which can be ignored by computers mining the text for data. Whilst we may not be able to fulfill the vision of the semantic web through (X)HTML, we can bring our coding practices closer to it, thus ensuring that our web pages have greater longetivity and compatibility with emerging Web 2.0 (and Web 3.0) technologies. Learning (X)HTML therefore requires learning the CSS alternatives to traditional (X)HTML forms of presentational markup. As a result, this tutorial will discuss some basic CSS syntax before introducing further (X)HTML techniques such as changing fonts or creating tables.