网络工程：双语－－语义Web

Semantic Web

   The vast amounts of computerized data contained on the World Wide Web would appear to be the largest body of information ever assembled. Certainly, the Web is a uniquely valuable tool for both research and the dissemination of ideas and knowledge. But the fact remains that the Web has been remarkably resistant to direct, effective, efficient use by computers.

   Tim Berners-Lee--the Oxford University graduate who invented the Web in 1989, wrote the first Web browser and server in 1990 and currently directs the World Wide Web Consortium --has a much grander vision for the Web of the future, which he calls the Semantic Web. The Semantic Web adds a metadata infrastructure of tags to define elements of information within Web pages, linking them so computers can extract meaning from widely separated data as easily as the Internet currently links individual documents. The Semantic Web will make it possible for machines, as well as people, to find, read, understand and use data over the Web to accomplish useful tasks. The Semantic Web will extend, not replace, the Web as we know it today.

   In some instances, we already use specialized software to work with carefully identified Web data, but this is the exception, not the rule. It takes people to surf the Web, shop online, make sense of search-engine results and decide which additional links to follow. The Semantic Web, once it becomes a functioning reality, will let a user launch an agent or process that will then proceed on its own, perhaps checking back with the user periodically as the work progresses.

   The Internet was originally created as a way for researchers to easily exchange computer data with one another. Although data traveled across the Internet in the form of bits and bytes, the basic unit of meaning, as far as the computer systems were concerned, was the file.

   That changed when the Web came into being. Berners-Lee built his Web around pages, which are documents written in HTML. A versatile language, HTML combines interactive forms, text and multimedia objects --such as images and sound--and it describes how these elements should be presented and what the overall page should look like. Unfortunately, HTML has a very limited ability to classify the blocks of text on a page, apart from the roles they play in a typical document's organization and in the chosen graphical layout.

   As Web use grew, HTML's limitations led to the development of XML and XHTML, which began to offer mechanisms for adding meaning to Web pages. The Simple Object Access Protocol and Web services became a reality, making it easier for users and even automated processes to gather specific information or perform specialized functions across the Web. When the Semantic Web comes to fruition, software will be able to locate information within Web pages, thus breaking through the document level and accessing real data that it can use directly. In one sense, the Semantic Web will become a kind of global database.