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xml介绍

原创 Linux操作系统 作者:ipqiaojj 时间:2009-03-31 15:05:00 0 删除 编辑
  1. Introduction to XML



    XML was designed to transport and store data.

    HTML was designed to display data.


    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.


    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. You must define your own tags
    • XML is designed to be self-descriptive
    • XML is a W3C Recommendation

    The Difference Between XML and HTML

    XML is not a replacement for HTML.

    XML and HTML were designed with different goals:

    • XML was designed to transport and store data, with focus on what data is.
    • HTML was designed to display data, with focus on how data looks.

    HTML is about displaying information, while XML is about carrying information.


    XML Does not DO Anything

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

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

    <note>
    Tove
    Jani
    Reminder
    Don't forget me this weekend!

    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 information wrapped in tags. Someone must write a piece of software to send, receive or display it.


    XML is Just Plain Text

    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.


    With XML You Invent Your Own Tags

    The tags in the example above (like and ) are not defined in any XML standard. These tags are "invented" 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

    ,

    , etc.).

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


    XML is Not a Replacement for HTML

    XML is a complement to HTML.

    It is important to understand that XML is not a replacement 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.


    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.


    XML is Everywhere

    We have been participating in XML development since its creation. It has been amazing 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 of the Web.

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

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