Referencing Already Defined Elements : Reference « XML Schema « XML Tutorial

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You can only reference element declarations within sequences, sets of choices, unordered groups, and named group definitions.
Each reference may contain distinct values for minOccurs and maxOccurs.
 

File: Data.xml
<?xml version="1.0"?>  
<library> 
  <book id="b0836217462" available="true"> 
    <isbn>1111111111</isbn> 
    <title lang="en">Java</title> 
    <author id="CMS"> 
      <name>name</name> 
      <born>1998-11-26</born> 
      <dead>2000-02-12</dead> 
    </author> 
    <character id="PP"> 
      <name>Swing</name> 
      <born>1996-08-22</born> 
      <qualification>Yes</qualification> 
    </character> 
    <character id="Web"> 
      <name>JSP</name> 
      <born>1997-10-04</born> 
      <qualification>No</qualification> 
    </character> 
  </book> 
</library> 

File: Schema.xsd  
<?xml version="1.0"?> 
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"> 
  <xs:element name="name" type="xs:string"/> 
  <xs:element name="qualification" type="xs:string"/> 
  <xs:element name="born" type="xs:date"/> 
  <xs:element name="dead" type="xs:date"/> 
  <xs:element name="isbn" type="xs:string"/> 
  <xs:attribute name="id" type="xs:ID"/> 
  <xs:attribute name="available" type="xs:boolean"/> 
  <xs:attribute name="lang" type="xs:language"/> 
  <xs:element name="title"> 
    <xs:complexType> 
      <xs:simpleContent> 
        <xs:extension base="xs:string"> 
          <xs:attribute ref="lang"/> 
        </xs:extension> 
      </xs:simpleContent> 
    </xs:complexType> 
  </xs:element> 
  <xs:element name="library"> 
    <xs:complexType> 
      <xs:sequence> 
        <xs:element ref="book" maxOccurs="unbounded"/> 
      </xs:sequence> 
    </xs:complexType> 
  </xs:element> 
  <xs:element name="author"> 
    <xs:complexType> 
      <xs:sequence> 
        <xs:element ref="name"/> 
        <xs:element ref="born"/> 
        <xs:element ref="dead" minOccurs="0"/> 
      </xs:sequence> 
      <xs:attribute ref="id"/> 
    </xs:complexType> 
  </xs:element> 
  <xs:element name="book"> 
    <xs:complexType> 
      <xs:sequence> 
        <xs:element ref="isbn"/> 
        <xs:element ref="title"/> 
        <xs:element ref="author" minOccurs="0" maxOccurs="unbounded"/>  
        <xs:element ref="character" minOccurs="0" 
          maxOccurs="unbounded"/> 
      </xs:sequence> 
      <xs:attribute ref="id"/> 
      <xs:attribute ref="available"/> 
    </xs:complexType> 
  </xs:element> 
  <xs:element name="character"> 
    <xs:complexType> 
      <xs:sequence> 
        <xs:element ref="name"/> 
        <xs:element ref="born"/> 
        <xs:element ref="qualification"/> 
      </xs:sequence> 
      <xs:attribute ref="id"/> 
    </xs:complexType> 
  </xs:element> 
</xs:schema>