Understand the definition of WEB page tool language XML (2)
Author：Eve Cole
Update Time：2009-07-07 16:10:01
2. Definition of XML
XML is a simplified version of SGML that combines the rich functionality of SGML with the ease of use of HTML into Web applications. XML retains the extensible capabilities of SGML, which makes XML fundamentally different from HTML. XML is much more powerful than HTML. It is no longer a fixed tag, but allows the definition of an unlimited number of tags to describe the information in the document, allowing nested information structures. HTML is just a general method for displaying data on the Web, while XML provides a general method for directly processing Web data. HTML focuses on describing the display format of a Web page, while XML focuses on describing the content of a Web page.
XML includes Extensible Format Language XSL (Extensible Style Language) and Extensible Linking Language XLL (Extensible Linking Language).
XSL is used to translate XML data into HTML or other formatted languages. XSL provides a stacked page CSS function, allowing developers to construct Web pages with an expression layer structure that is different from the data structure of XML. XSL can also be used with HTML to construct stacked pages. XSL can interpret an unlimited number of tags, which makes the Web layout more colorful, such as dynamic text and horse racing text. In addition, XSL also handles multiple languages, double-byte Chinese character display, various processing of grids, etc.
XLL is the link language of XML, which is similar to the link of HTML, but has more powerful functions. XLL supports extensible links and multi-directional links. It breaks the restriction that HTML only supports the simplest links under the concept of hypertext, and can support address-independent domain names, two-way links, loops, collection links from multiple sources, etc. XLL links are not restricted by documents and can be specified and managed completely according to user requirements.
In order to make XML easy to learn and use, XML simplifies a large number of functions that are rarely used in SGML. Just as only eight thousand of the hundreds of thousands of Chinese characters are commonly used, and the commonly used parts of SGML only account for 20%, XML abandons the uncommon parts of SGML, making it 80% streamlined at once. As a result, the syntax specification for XML is only 30 pages, while SGML is 500 pages.
XML design also considers its ease of use, which comes from two aspects: on the one hand, it is convenient for users to write Web pages, and on the other hand, it is not difficult for designers to implement XML browsers.
In short, XML uses a simple and flexible standard format to provide an effective means for describing data and exchanging data for Web-based applications. HTML describes a common method for displaying global data, while XML provides a common method for directly processing global data.
