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XML基础:Introduction to XML

XMLHTMLWebJavaScript 
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Introduction to XML


XML was designed to transport(传输) and store data.
HTML was designed to display data.

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What You Should Already Know

Before you continue you should have a basic understanding of the following:

HTML
JavaScript

If you want to study these subjects first, find the tutorials on our Home page.

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What is XML?

XML stands for EXtensible Markup Language
XML is a markup language much like HTML
XML was designed to carry data, not to display data
XML tags are not predefined(预先确定). You must define your own tags
XML is designed to be self-descriptive(自我解释)
XML is a W3C Recommendation(推荐)

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The Difference Between XML and HTML

1.XML is not a replacement for HTML.
2.XML and HTML were designed with different goals:
3.XML was designed to transport and store data, with focus on what data is.
4.HTML was designed to display data, with focus on how data looks.
5.HTML is about displaying information, while XML is about carrying information.

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XML Does not DO Anything

Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure(组织), store(存储), and transport(传输) information.

The following example is a note to Tove from Jani, stored as XML: 

<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>


The note above is quite self descriptive. It has sender and receiver information, it also has a heading and a message body.

But still, this XML document does not DO anything. It is just pure(纯的) information wrapped in(被...包围) tags. Someone must write a piece of software to send, receive or display it.

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XML is Just Plain Text(纯文本)

XML is nothing special. It is just plain text. Software that can handle plain text can also handle XML.

However, XML-aware applications can handle the XML tags specially. The functional meaning of the tags depends on the nature of the application.

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With XML You Invent Your Own Tags

The tags in the example above (like <to> and <from>) are not defined in any XML standard. These tags are "invented"(创造) by the author of the XML document.
That is because the XML language has no predefined tags.

The tags used in HTML (and the structure of HTML) are predefined. HTML documents can only use tags defined in the HTML standard (like <p>, <h1>, etc.).

XML allows the author to define his own tags and his own document structure.

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XML is Not a Replacement for HTML

XML is a complement(补充) to HTML.

It is important to understand that XML is not a replacement(更换) for HTML. In most web applications, XML is used to transport data, while HTML is used to format and display the data.

My best description of XML is this:

XML is a software and hardware independent tool for carrying information.

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XML is a W3C Recommendation
XML became a W3C Recommendation 10. February 1998.

To read more about the XML activities at W3C, please read our W3C Tutorial(www.w3schools.com).

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XML is Everywhere

We have been participating in(参加) XML development since its creation. It has been amazing(令人惊异的) to see how quickly the XML standard has developed, and how quickly a large number of software vendors have adopted the standard.

XML is now as important for the Web as HTML was to the foundation(基础) of the Web.

XML is everywhere. It is the most common tool for data transmissions(数据传输) between all sorts of applications, and is becoming more and more popular in the area of storing and describing information.

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