<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE students 
[
      <!ELEMENT students (student*)>
      <!ELEMENT student (name+,class+,number+,duty*,sex+,hometown?)>
      <!ELEMENT name (#PCDATA)>
      <!ELEMENT class (#PCDATA)>
      <!ELEMENT number (#PCDATA)>
      <!ELEMENT duty (#PCDATA)>
      <!ELEMENT sex (#PCDATA)>
      <!ELEMENT hometown (province?,city?)>
      <!ELEMENT province (#PCDATA)>
      <!ELEMENT city (#PCDATA)>
]>

<students>
  
   <student>
      <name>张三</name>
      <class>1406401</class>
      <number>1406401-01</number>
      <duty>团支书</duty>
      <sex>男</sex> 
      <hometown>
        <province>湖南省</province>
        <city>长沙市</city>
       </hometown>
   </student>
   
   <student>
      <name>李四</name>
      <class>1406101</class>
      <number>1406101-02</number>
      <duty>学习委员</duty>
      <sex>女</sex> 
       <hometown>
        <city>北京</city>
        </hometown>
   </student>
   
   <student>
      <name>王五</name>
      <class>1406402</class>
      <number>1406402-03</number>
      <sex>男</sex>
       <hometown>
        <province>山西省</province>
        <city>大同市</city>
       </hometown>
   </student>
   
   <student>
      <name>孙六</name>
      <class>1406401</class>
      <number>1406401-04</number>
      <sex>男</sex>
       <hometown>
        <province>湖北省</province>
        <city>武汉市</city>
       </hometown>
   </student>
  
   <student>
      <name>赵七</name>
      <class>1406102</class>
      <number>1406102-05</number>
      <duty>班长</duty>
      <sex>男</sex> 
       <hometown>
        <province>湖南省</province>
        <city>益阳市</city>
       </hometown>
   </student>
  

</students>