计算机科学论坛--The introduction of XML

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XML is a way of adding intelligence to your documents. It lets you identify each element using meaningful tags and it lets you add information ("metatdata") about each element.

XML is very much a part of the future of Web, and part of the future for all electronic information.

XML is a syntax for marking up data and it works with many other technologies to display and process information. It looks and feels very much like HTML.

XML isn't going to replace everything else you've already learned; it complements it and extends it.

XML isn't going to change the way your Web pages look. You'll still need to use CSS--Cascading Style Sheets-- (with XML) to define font colors or JavaScript (again, with XML) to make your images fly around. Yet XML will change the way you and others read documents and it will change the way documents are filed and stored. It's a new technology and you certainly don't need to use it in order to build a great Web site -- but you will want to be aware of it as you look at the Web of the future.

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Where Did XML Come From?

XML is a simplified version of SGML and a cousin of HTML. It was developed by members of the W3C and released as a recommendation by the W3C in February 1998.

SGML, the parent of XML, is an international standard that has been in use as a markup language primarily for technical documentation and government applications since the early 1980s. It was developed to standardize the production process for large document sets. Think: Medical records. Company databases. Aircraft parts catalogs. Other really huge documents.

Marking-up documents in SGML allows information to be passed from one system to the next without losing information. With databases marked-up in SGML you can see what Widget A is all about and go check to see if Widget A is in stock.

Early on, people thought that SGML would be useful for the Web. In fact, HTML is really an very basic application of SGML! But HTML quickly became used for visual layout, so a group of people returned to the basics, determined to create something that had the strengths of SGML without being so difficult to implement -- and had the ease of use of HTML, but with more structural power. The result was XML.

The design goals of XML, taken from the XML Specification are:

XML shall be straightforwardly usable over the Internet.
XML shall support a wide variety of applications.
XML shall be compatible with SGML.
It shall be easy to write programs which process XML documents.
The number of optional features in XML is to be kept to the absolute minimum, 　　　ideally zero.
XML documents should be human-legible and reasonably clear.
The XML design should be prepared quickly.
The design of XML shall be formal and concise.
XML documents shall be easy to create.
Terseness in XML markup is of minimal importance.

In other words, XML is easy to create, easy to read, and designed for use over the Internet. What more could a Web designer ask for?

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I'm going to study it, but is it too difficlt for me?


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