##XML声明

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<?xml version="1.0" encoding="UTF-8" ?>  <!-- 注释：version 版本号  encoding 编码 -->

##特殊字符处理

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1.实体引用
&lt;    <   小于
&gt;    >   大于
&amp;   &.  和号
&apos;  '   单引号
&quot;  "   双引号
2.CDTA标签
<![CDATA[" xml代码 "]]>
eg:<fff>
		<![CDATA[
			<a href="https://www.baidu.com">百度</a>
		]]>
	</fff>

DTD语义约束 XML `

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<!ELEMENT>  <!-- 定义xml文档中允许出现的节点以及数量 -->
eg:<!ELEMENT hr (employee)>   <!--定义hr节点只允许出现一个emplyee子节点-->
<!ELEMENT hr(employee+)>   <!--定义hr节点最少出现一个emplyee子节点-->
<!ELEMENT hr(employee*)>   <!--定义hr节点0个或多个emplyee子节点-->
<!ELEMENT hr (employee?)>   <!--定义hr节点要么一个要么多个emplyee子节点-->
<!ELEMENT hr (name,age,address)>   <!--定义hr下name,age,address子节点-->
<!ELEMENT name(#PCDATA)>  <!-- 当前节点是纯文本格式 -->

<!DOCTYPE 根节点 SYSTEM "dtd文件路径">  <!--XML种引入DTD文件-->
eg:<!DOCTYPE hr SYSTEM "hr.dtd">

<!ATTLIST 节点 属性 CDATA "描述">
eg:<!ELEMENT employee no CDATA ""> <!--employee节点no属性-->

##DTD例子

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hr SYSTEM "hr.dtd">
<hr>
	<employee no="001">
		<name>joy</name>
		<age>20</age>
		</address>测试地址1</address>
    <other>
			<realyName>张三</realyName>
    </other>
	</employee>
	<employee no="002">
		<name>lucyy</name>
		<age>40</age>
		</address>测试地址2</address>
    <other>
			<realyName>李四</realyName>
    </other>
	</employee>
</hr>

<!--dtd文件 hr.dtd-->
<!ELEMENT hr (employee+)>
<!ELEMENT employee (name,age,address,other)>
<!ATTLIST employee no CDATA "">
<!ELEMENT name (#PCDATA)>
<!ELEMENT age (#PCDATA)>
<!ELEMENT address (#PCDATA)>
<!ELEMENT other (realyName)>
<!ELEMENT realyName (#PCDATA)>

##Schema语义约束 XML 

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<?xml version="1.0" encoding="UTF-8"?>
<hr xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="hr.xsd">
	<employee no="001">
		<name>joy</name>
		<age>20</age>
		</address>测试地址1</address>
    <other>
			<realyName>张三</realyName>
    </other>
	</employee>
	<employee no="002">
		<name>lucyy</name>
		<age>40</age>
		</address>测试地址2</address>
    <other>
			<realyName>李四</realyName>
    </other>
	</employee>
</hr>

<!-- hr.xsd文件 -->
<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema">
	<element name="hr">
  	<complexType>
    	<sequence>
      	<element name="employee" minOccurs="1" maxOccurs="999">
          <complexType>
          	<sequence>
              <element name="name" type="string"></element>
              <element name="age" type="integer"></element>
              <element name="age"> <!--age 进行范围限定的写法-->
             		<simpleType>
                	<restriction base="integer">
                  	<minInclusive value="18"></minInclusive>
                    <maxInclusive value="60"></maxInclusive>
                  </restriction>
                </simpleType>
              </element>
              <element name="address" type="string">
                <complexType>
                  <sequence>
                    <element name="other">
                      <element name="realyName" type="string"></element>
                    </element>
                  </sequence>
                </complexType>
              </element>
            </sequence>
            <attribute name="no" type="string" use="required"></attribute>
          </complexType>   
        </element>
      </sequence>
    </complexType>
  </element>
</schema>