Simplifying the Library (XML Schema)

8.4. Simplifying the Library

Our library, with its single instance document, doesn't really deserve redefinition, so we will just use inclusion to isolate simple and complex type definitions in their own schemas to keep these schemas shorter. To do this, we can create a partial schema to define all our simple types:

<?xml version="1.0"?> 
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:simpleType name="string255">
    <xs:restriction base="xs:token">
      <xs:maxLength value="255"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="string32">
    <xs:restriction base="xs:token">
      <xs:maxLength value="32"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="isbn">
    <xs:restriction base="xs:unsignedLong">
      <xs:totalDigits value="10"/>
      <xs:pattern value="\d{10}"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="bookID">
    <xs:restriction base="xs:ID">
      <xs:pattern value="b\d{10}"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="supportedLanguages">
    <xs:restriction base="xs:language">
      <xs:enumeration value="en"/>
      <xs:enumeration value="es"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="date">
    <xs:restriction base="xs:date">
      <xs:pattern value="[^:Z]*"/>
    </xs:restriction>
  </xs:simpleType>
</xs:schema>

We can then create a second schema containing all the complex type definitions (note that this second schema doesn't need to include the simple type definitions that will be included directly into the main schema):

<?xml version="1.0"?> 
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:complexType name="elementWithID">
    <xs:attribute ref="id"/>
  </xs:complexType>
  <xs:complexType name="bookTmp">
    <xs:complexContent>
      <xs:extension base="elementWithID">
        <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="available"/>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
  <xs:complexType name="personType">
    <xs:complexContent>
      <xs:extension base="elementWithID">
        <xs:sequence>
          <xs:element ref="name"/>
          <xs:element ref="born"/>
          <xs:element ref="dead" minOccurs="0"/>
          <xs:element ref="qualification" minOccurs="0"/>
        </xs:sequence>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
</xs:schema>

We can leave all the other definitions in our main schema, which includes (using xs:include) the schemas containing the simple and complex type definitions:

<?xml version="1.0"?> 
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:include schemaLocation="simpleTypes.xsd"/>
  <xs:include schemaLocation="complexTypes.xsd"/>
  <xs:element name="name" type="string32"/>
  <xs:element name="qualification" type="string255"/>
  <xs:element name="born" type="date"/>
  <xs:element name="dead" type="date"/>
  <xs:element name="isbn" type="isbn"/>
  <xs:attribute name="id" type="xs:ID"/>
  <xs:attribute name="available" type="xs:boolean"/>
  <xs:attribute name="lang" type="supportedLanguages"/>
  <xs:element name="title">
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="string255">
          <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="book">
    <xs:complexType>
      <xs:complexContent>
        <xs:restriction base="bookTmp">
          <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 name="id" type="bookID"/>
          <xs:attribute ref="available"/>
        </xs:restriction>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  <xs:element name="author">
    <xs:complexType>
      <xs:complexContent>
        <xs:restriction base="personType">
          <xs:sequence>
            <xs:element ref="name"/>
            <xs:element ref="born"/>
            <xs:element ref="dead" minOccurs="0"/>
          </xs:sequence>
          <xs:attribute ref="id"/>
        </xs:restriction>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
  <xs:element name="character">
    <xs:complexType>
      <xs:complexContent>
        <xs:restriction base="personType">
          <xs:sequence>
            <xs:element ref="name"/>
            <xs:element ref="born"/>
            <xs:element ref="qualification"/>
          </xs:sequence>
          <xs:attribute ref="id"/>
        </xs:restriction>
      </xs:complexContent>
    </xs:complexType>
  </xs:element>
</xs:schema>