Background of WEB page tool Language XML

Like HTML, XML comes from StandardGeneralizedMarkupLanguage, which is a general Markup Language (SGML) for scale. Before the Web was invented, SGML already existed. As its name implies, SGML is a general language that uses tags to describe document materials.

Like HTML, XML comes from Standard Generalized Markup Language (SGML. Before the Web was invented, SGML already existed. As its name implies, SGML is a common language for describing document materials with tags. it contains a series of document type definitions (DTD for short ), the DTD defines the meaning of the tag, so the syntax of SGML can be expanded. SGML is very ambitious, not easy to learn, but not easy to use, it is also very difficult to implement in the computer. In view of these factors, researchers at the European nuclear physics research center, the inventor of Web, proposed the HTML language based on the current (1989) computer skills.

HTML only applies a small part of the SGML tag. for example, HTML 3.2 defines 70 tags. To facilitate the implementation on the computer, the HTML mark is fixed, that is, the HTML syntax cannot be expanded, and it does not need to contain DTD. The fixed syntax of HTML makes it easy to learn and use. it is also very easy to develop HTML browsers on the computer. It is precisely because of the simplicity of HTML that Web technology is moving from the computer industry to the whole society, to thousands of households, the development of Web is booming.

In recent years, as the use of Web becomes more and more extensive and deeper, people gradually feel that HTML is not enough, and the syntax of HTML is too simple seriously hinders the use of it to express the complex situation. Although HTML has released a new version and has the functions of expressing scripts, tables, and frames, it cannot meet the ever-increasing demands. On the other hand, in the past few years, the development of computer technology has been very agile, and it has been able to implement a Web browser that is much more complex than when HTML was invented, therefore, developing a new Web page language is both necessary and possible.

Some people suggest directly using SGML as the Web language, which can solve the difficulties encountered by HTML. However, SGML is too ambitious, and it is inconvenient for users to learn and apply it. it is very difficult to fully implement the SGML browser. Therefore, we will naturally think of only applying the subset of SGML, make the new language easy to use and implement. In this situation, W3C recommends that a simplified SGML version -- XML be applied to the Web scale organization.