Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

Hypermedia and hypertext are nonlinear information, presented to users in a way that lets them jump from one reference to another with the click of a button. On the Internet and the World Wide Web, people use hypermedia to access all sorts of information. The technology made using computers as easy as driving cars. Hypertext is linked text information, while hypermedia is both linked text and multimedia (graphics, sound, video, animation, and so on) information. The difference is trivial and most Web documents are now hypermedia documents. Hypermedia is well understood. This topic provides historical information, defines the terminology, and identifies related technologies.

Hypermedia is all about hyperlinking: while browsing through a hypermedia document, you can select a link and quickly jump to a reference or another source of information, and then jump back and continue reading where you left off. Vannevar Bush first suggested using electronic technology to access cross-links and references in an article that appeared in the August 1945 issue of Atlantic Monthly!

Ted Nelson actually coined the term hypertext back in 1965 and created a vision for a project called "Xanadu" that would implement hypertext on a Sun workstation. I heard Nelson speak about Xanadu in the early 1980s-how it would handle copyright laws and payments to authors for referenced works. I'm not sure if Ted Nelson was thinking about the Web when he came up with ideas, but he was certainly on the right track.

The most important feature is hyperlinking. With it, Web site authors can include the following kinds of links:

• Links to other sections on the same document    A common practice is to build a table of contents at the beginning of a Web document. When you click an item in the table, you will jump to a lower section in the document.


• Links to other documents at the same Web site    A hyperlink that opens another document at the same Web site, sometimes in a different directory.


• Links to documents at other Web sites    These require that the full URL to other Web sites be embedded in the HTML document.

One of the unifying concepts of the Internet is that all the documents stored on Web servers are created with HTML (and now XML). The HTML language is based on some early work done by IBM, and takes into account the fact that most documents have similar features. For example, the title is usually a large bold font, and the text is a smaller font with occasional underlined or italicized elements. In the late 1980s, IBM developed GML (Generalized Markup Language) as a way to tag or mark these elements so that documents could be moved from one place to another and retain their formatting.

GML is designed to be a universal document language. It was even standardized by the International Standards Organization, which called it SGML (Standard Generalized Markup Language). Tim Berners-Lee derived HTML from SGML in 1990 when he put together the first proposals for the World Wide Web.

The other component that makes hypermedia work on the Web is HTTP (Hypertext Transfer Protocol). HTTP is the protocol that Web browsers and Web servers use to set up a connection and exchange information. When a Web browser accesses a Web server, it requests a specific HTML page on that server. The server then responds by sending the page to the client using HTTP protocols.

XML is the latest Web development, and potentially the most significant. It goes beyond HTML by allowing developers to tag information in documents. With XML, if a document contains an address, it will be tagged as "Address." Other programs can then search the document for "Address" and extract the value stored there. XML documents are true information documents with the same benefits as database files or spreadsheets. With standard HTML documents, if you wanted to extract some information, you had to resort to cut-and-paste techniques. With XML, your database program can automatically extract information. What XML does is allow Web documents to participate directly in business applications, electronic commerce, and workflow applications. See "XML (Extensible Markup Language)."

Another interesting development is DAV (Distributed Authoring and Version), which is a set of extensions to HTTP that allows distributed Web authoring tools to perform, in an interoperable manner, versioning and configuration management of Web resources. See "WebDAV."

Yet another interesting development is Webcasting, which allows users to receive Web pages, updates, and broadcasts by subscribing to a service. Broadcasts can include multimedia audio and video. See "Webcasting."

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.