Understand the background of WEB page tool language XML (1)
Author：Eve Cole
Update Time：2009-07-07 16:10:04
1. Background of XML
XML, like HTML, comes from Standard Generalized Markup Language, or SGML for short. SGML existed long before the Web was invented. As its name suggests, SGML is a universal language that uses tags to describe document materials. It contains a series of document type definitions (DTDs for short). The meaning of tags is defined in the DTD, so the syntax of SGML is extensible. of. SGML is very large, neither easy to learn nor easy to use, and it is also very difficult to implement on a computer. In view of these factors, researchers at CERN, the inventor of the Web, proposed the HTML language based on the capabilities of computer technology at the time (1989).
HTML only uses a small part of the tags in SGML. For example, HTML 3.2 defines 70 tags. In order to facilitate implementation on a computer, the tags specified by HTML are fixed, that is, the HTML syntax is not extensible, and it does not need to contain a DTD. The fixed syntax of HTML makes it easy to learn and use, and it is also very easy to develop an HTML browser on a computer. It is precisely because of the simplicity of HTML that Web technology has moved from the computer world to the entire society and to millions of households. The development of the Web is booming.
In recent years, as the application of the Web becomes more and more extensive and in-depth, people gradually feel that HTML is not enough. The overly simple syntax of HTML seriously hinders the use of it to express complex forms. Although HTML has launched new versions one after another, and already has expression functions such as scripts, tables, frames, etc., it has never been able to meet the growing demand. On the other hand, computer technology has developed very rapidly in recent years, and it has been possible to implement a web browser that is much more complex than when HTML was originally invented. Therefore, it is both necessary and possible to develop a new web page language.
Some people suggest using SGML directly as the Web language, which can certainly solve the difficulties encountered by HTML. However, SGML is too large and inconvenient for users to learn and use. It is very difficult to fully implement SGML in a browser, so it is natural to think of using only a subset of SGML to make the new language both convenient to use and easy to implement. It was under this situation that the Web standardization organization W3C recommended the use of a streamlined version of SGML - XML came into being.
