XML Schema

Chapter 3. Giving Some Depth to Our First Schema

Our first schema was very flat, and all its components were defined at the top level. Our second attempt will give it more depth and show how local components may be defined.

Working From the Structure of the Instance Document

For this second schema, we follow a style opposite from the one we used in Chapter 2, and we define all the elements and attributes locally where they appear in the document.

Following the document structure, we will start by defining our document element library. This element was defined in the earlier schema as:

<xs:element name="library">
  <xs:complexType>
    <xs:sequence>
      <xs:element ref="book" maxOccurs="unbounded"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

In our new schema, we will keep the same construct and the same structure, but we will replace the reference to the book element with the actual definition of this element:

<xs:element name="library">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="book" maxOccurs="unbounded">
        <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:sequence>
  </xs:complexType>
</xs:element>

Because the definition of the book element is contained inside the definition of the library element, other definitions ...