Web Basics


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Copyright 2000 by Greg Reddick

Go to Part I: Internet Basics

 The World Wide Web (or just Web) is a combination of several technologies built on top of the internet. It is a protocol, a markup language, a program that interprets that markup language, and a program that serves up the files. The protocol is HTTP, discussed above. The main markup language is HTML, the program is a Web Browser, and the program that serves up the files is a Web Server. All of these are discussed below. The organization that forms and approves Web standards is the World Wide Web Consortium, or W3C. [http://www.w3.org]

 A markup language is a way of placing information about the meaning of a document into the document itself. The granddaddy of all the markup languages used on the web today is Standard Generalized Markup Language, or SGML. SGML was developed at IBM in the 1970s, and was adopted as an ISO (International Standards Organization) standard in 1986, as ISO8879. [Unfortunately, and stupidly, ISO doesn't publish their standards on the web. You can buy the ISO8879 standard at the ISO web site for a small fortune. For a more accessible overview of SGML, see http://www.oasis-open.org/cover/general.html.] SGML is extremely general. It allows you to specify a set of valid tags that can be placed into a document, then use those tag to markup the document. Tags are markers such as <p>This is a paragraph.</p> that tell the thing that understands the document what it should do with the text. In SGML, tag are surrounded with angle brackets, as in <tag>. A tag may be modified in some way by using attributes. Attributes are something that modifies the tag in some way. For example, <p align="center">This is a paragraph</p>. The align attribute modifies the p tag to tell it that it should center the paragraph. The end of some tagged text is marked by the same tag preceded by a slash. In SGML, a Document Type Definition, or DTD, defines what tags and attributes are valid in a document.

 In 1990, Tim Berners-Lee took four existing technologies, modified them slightly for his purposes, and produced the Web. The first of these was a modification of the FTP protocol to produce HTTP, a protocol for exchanging packets of information containing HTML. HyperText Markup Language, or HTML, is a particular DTD of SGML that recognizes a limited set of tags and attributes. Those tags tell a Web Browser how to display a document. There have been several versions of the HTML specification, but the latest one is HTML 4.01 (although see XHTML below). [http://www.w3.org/TR/REC-html40 ] HTML is moved from a Web Server to a Web Browser using HTTP. The Web Browser then interprets the HTML and renders a representation of it.

 Topics to come

  • Web Standards
    • CSS
    • DHTML
    • ECMAScript (JavaScript)
    • XML
    • XSL
    • XHTML
    • Etc.

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