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Specific example code sharing of XML and Schema namespaces

黄舟

Release： 2017-04-01 13:55:43

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The above describes XML and SchemaSome related contents of the namespace are introduced in detail. Let’s learn more about it through examples:

Example 1: Key points to understand Related concepts of namespace

The following example is an XML Schema file named "note.xsd"

<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com"
xmlns="http://www.w3schools.com"
elementFormDefault="qualified">
<xsd:element name="note">
      <xsd:complexType>
         <xsd:sequence>
           <xsd:element name="to" type="xs:string"/>
           <xsd:element name="from" type="xs:string"/>
           <xsd:element name="heading" type="xs:string"/>
           <xsd:element name="body" type="xs:string"/>
        </xsd:sequence>
      </xsd:complexType>
</xsd:element>
</xsd:schema>

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The XML document below and the one given above The XML Schema is associated with it, named "note.xml", and the following discussion will focus on these two documents

. #

<?xml version="1.0"?>
<note xmlns="http://www.w3schools.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3schools.com note.xsd">
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don&#39;t forget me this weekend!</body>
</note>

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This fragment: xmlns:xsd="
www.w3.org/2001/XMLSchema", indicating that this schema is used The elements and datatypes come from the "www.w3.org/2001/XMLSchema" namespace (it also indicates that they come from "www.w3.org". /2001/XMLSchema"Namespace elements and data types must be used with "xsd: " prefix. As a namespace identifier (in a declaration as a prefix to an element or attribute), you can also use it without xsd or xsi. This xmlns attribute contains basic XML schema elements, such as element, attribute, complexType, group, simpleType, etc. ## For any XML Schema definition document (XSD), there is a top-level schema (XSD) element. The definition must include this namespace:

www.w3.org/2001/XMLSchema

. That is, this namespace is the standard namespace defined by the XML Schema specification - all XML Schema elements must belong to this namespace ##. # This fragment: targetNamespace="www.w3schools.com" indicates this schema The elements defined by (note, to, from, heading, body) come from the "www.w3schools.com
" namespace. The targetNamespace attribute represents the URI of the namespace corresponding to the schema. That is to say, the namespace must be declared in other documents (including its own document) that reference the Schema, and its URI should be the attribute value of targetNamespace. For example, here we need to use the extended data type defined by note.xsd (note, to, from, heading, body), so the namespace xmlns="www.w3schools.com" is also declared. And that namespace is the default namespace (no prefix). The targetNamespace attribute declares an XML namespace for all new types explicitly created in the schema. Let’s look at what the beginning of the XML document note.xml specified by this schema will look like:

<note xmlns="http://www.w3schools.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3schools.com note.xsd">

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其中缺省名称空间声明xmlns="www.w3schools.com"就是和刚刚声明的XML Schema的名称空间相结合来规定该XML文档。（即该文档用到了此名称空间中定义的数据） xmlns:xsi="www.w3.org/2001/XMLSchema-instance" 是任何XML实例文档固有的XML模式实例名称空间，它由XML模式规范定义。而xsi:schemaLocation="www.w3schools.com note.xsd"则规定了该名称空间所对应的schema的位置，即在相同路径的note.xsd文件。

例二：重点理解Schema文档使用自身定义类型

xsd文件中定义了一个targetNameSpace后，其内部定义的元素，属性，类型等都属于该targetNameSpace,其自身或外部xsd文件使用这些元素，属性等都必须从定义的targetNameSpace中找。修改一下note.xsd，去除默认名称空间的声明，并添加一个复杂类型：

<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com"
elementFormDefault="qualified">
<xsd:element name="note">
      <xsd:complexType>
        <xsd:sequence>
       <xsd:element name="to" type="xs:string"/>
       <xsd:element name="from" type="xs:string"/>
<xsd:element name="heading" type="xs:string"/>
       <xsd:element name="body" type="xs:string"/>
       </xsd:sequence>
      </xsd:complexType>
</xsd:element>
<xsd:element name="Student" type="stu"/> 
  <xsd:complexType name="stu"> 
  <xsd:sequence> 
   <xsd:element name="Name" type="xs:string"/> 
   <xsd:element name="Class" type="xs:string"/> 
  </xsd:sequence> 
 </xsd:complexType> 
</xsd:schema>

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上述代码中，复杂类型stu是找不到的，因为你定义了一个名称空间"www.w3schools.com",该复杂类型存在于"www.w3schools.com"中，因此应该修改代码如下：

<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com"
xmlns:student="http://www.w3schools.com"
elementFormDefault="qualified">
<xsd:element name="note">
      <xsd:complexType>
        <xsd:sequence>
       <xsd:element name="to" type="xs:string"/>
       <xsd:element name="from" type="xs:string"/>
<xsd:element name="heading" type="xs:string"/>
       <xsd:element name="body" type="xs:string"/>
       </xsd:sequence>
      </xsd:complexType>
</xsd:element>
<xsd:element name="Student" type="student:stu"/> 
  <xsd:complexType name="stu"> 
  <xsd:sequence> 
   <xsd:element name="Name" type="xs:string"/> 
   <xsd:element name="Class" type="xs:string"/> 
  </xsd:sequence> 
 </xsd:complexType> 
</xsd:schema>

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若自身并不使用重用组件，仅供外部使用的话，则只定义targetNameSpace就可以，不用指定别名。
通过上面的例子，我们可以很深刻的理解targetNameSpace。targetNamespace定义了Schema定义的新元素与属性的名称空间。而"www.w3.org/2001/XMLSchema"名称空间则定义了element, attribute, complexType, group, simpleType等元素。

理解了上面的两个例子，Schema的命名空间的内容应该就明了了。

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