IT博客-Favor Soup | 反胃书屋-随笔分类-XML相关http://www.cnitblog.com/dickznew/category/5061.html斯是陋室，惟吾德馨。zh-cnSun, 02 Oct 2011 02:31:04 GMTSun, 02 Oct 2011 02:31:04 GMT60XML Beginner notes (2)http://www.cnitblog.com/dickznew/archive/2007/04/04/25159.htmlD主D主Wed, 04 Apr 2007 08:37:00 GMThttp://www.cnitblog.com/dickznew/archive/2007/04/04/25159.htmlhttp://www.cnitblog.com/dickznew/comments/25159.htmlhttp://www.cnitblog.com/dickznew/archive/2007/04/04/25159.html#Feedback0http://www.cnitblog.com/dickznew/comments/commentRss/25159.htmlhttp://www.cnitblog.com/dickznew/services/trackbacks/25159.htmlXML Schema is an XML-based alternative to DTD.
An XML schema describes the structure of an XML document.
The XML Schema language is also referred to as XML Schema Definition (XSD).

What is an XML Schema?

The purpose of an XML Schema is to define the legal building blocks of an XML document, just like a DTD.
An XML Schema:

  • defines elements that can appear in a document
  • defines attributes that can appear in a document 
  • defines which elements are child elements 
  • defines the order of child elements
  • defines the number of child elements
  • defines whether an element is empty or can include text
  • defines data types for elements and attributes 
  • defines default and fixed values for elements and attributes

XSL

It started with XSL and ended up with XSLT, XPath, and XSL-FO.

It Started with XSL

XSL stands for EXtensible Stylesheet Language.

The World Wide Web Consortium (W3C) started to develop XSL because there was a need for an XML-based Stylesheet Language.

CSS = HTML Style Sheets

HTML uses predefined tags and the meaning of the tags are well understood.
The <table> element in HTML defines a table - and a browser knows how to display it.
Adding styles to HTML elements is simple. Telling a browser to display an element in a special font or color, is easy with CSS.


XSL = XML Style Sheets

XML does not use predefined tags (we can use any tag-names we like), and the meaning of these tags are not well understood.
The <table> element in HTML defines a table - and a browser knows how to display it.
Adding styles to HTML elements is simple. Telling a browser to display an element in a special font or color, is easy with CSS.

XSL - More Than a Style Sheet Language

XSL consists of three parts:

  • XSLT - a language for transforming XML documents
  • XPath - a language for navigating in XML documents
  • XSL-FO - a language for formatting XML documents


 



D主 2007-04-04 16:37 发表评论
]]>XML Beginner notes (1)http://www.cnitblog.com/dickznew/archive/2007/04/04/25156.htmlD主D主Wed, 04 Apr 2007 08:20:00 GMThttp://www.cnitblog.com/dickznew/archive/2007/04/04/25156.htmlhttp://www.cnitblog.com/dickznew/comments/25156.htmlhttp://www.cnitblog.com/dickznew/archive/2007/04/04/25156.html#Feedback0http://www.cnitblog.com/dickznew/comments/commentRss/25156.htmlhttp://www.cnitblog.com/dickznew/services/trackbacks/25156.htmlXML was designed to describe data and to focus on what data is while HTML was designed to display data and to focus on how data looks.
XML was designed to describe data, its tags are not predefined. You must define your own tags. XML uses a Document Type Definition (DTD) or an XML Schema to describe the data.
Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store and to send information.
XML Namespaces provide a method to avoid element name conflicts.
Since element names in XML are not predefined, a name conflict will occur when two different documents use the same element names.
EXAMPLES:
This XML document carries information in a table:
<table>
   <tr>
       <td>Apples</td>
       <td>Bananas</td>
   </tr>
</table>
This XML document carries information about a table (a piece of furniture):
<table>
    <name>African Coffee Table</name> 
    <width>80</width> 
    <length>120</length>
</table>
If these two XML documents were added together, there would be an element name conflict because both documents contain an element with different content and definition.

Solving Name Conflicts Using a Prefix
This XML document carries information in a table: 
<h:table>
   <h:tr>
   <h:td>Apples</h:td>
   <h:td>Bananas</h:td>

   </h:tr>
</h:table>
This XML document carries information about a piece of furniture: 
<f:table>
   <f:name>African Coffee Table</f:name>
   <f:width>80</f:width>

   <f:length>120</f:length>
</f:table>
Now there will be no name conflict because the two documents use a different name for their <table > element ( <h:table > and < f:table >). By using a prefix, we have created two different types of < table > elements.

Using Namespaces

This XML document carries information in a table:

<h:table xmlns:h="http://www.w3.org/TR/html4/">
   <h:tr>

   <h:td>Apples</h:td>
   <h:td>Bananas</h:td>
   </h:tr>
</h:table>

This XML document carries information about a piece of furniture:

<f:table xmlns:f="http://www.w3schools.com/furniture">
   <f:name>African Coffee Table</f:name>
   <f:width>80</f:width>
   <f:length>120</f:length>

</f:table>

Instead of using only prefixes, we have added an xmlns attribute to the <table> tag to give the prefix a qualified name associated with a namespace.

The XML Namespace (xmlns) Attribute

The XML namespace attribute is placed in the start tag of an element and has the following syntax:

xmlns:namespace-prefix="namespaceURI"

When a namespace is defined in the start tag of an element, all child elements with the same prefix are associated with the same namespace.

Note that the address used to identify the namespace is not used by the parser to look up information. The only purpose is to give the namespace a unique name. However, very often companies use the namespace as a pointer to a real Web page containing information about the namespace.

 

Uniform Resource Identifier (URI)

A Uniform Resource Identifier (URI) is a string of characters which identifies an Internet Resource.
The most common URI is the Uniform Resource Locator (URL) which identifies an Internet domain address. Another, not so common type of URI is the Universal Resource Name (URN). In our examples we will only use URLs.

Default Namespaces

Defining a default namespace for an element saves us from using prefixes in all the child elements. It has the following syntax:

xmlns="namespaceURI"

This XML document carries information in a table:

<table xmlns="http://www.w3.org/TR/html4/">

   <tr>
   <td>Apples</td>
   <td>Bananas</td>
   </tr>
</table>

This XML document carries information about a piece of furniture:

<table xmlns="http://www.w3schools.com/furniture">
   <name>African Coffee Table</name>
   <width>80</width>

   <length>120</length>
</table>



D主 2007-04-04 16:20 发表评论
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