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XSD Complex Elements

A complex element contains other elements and/or attributes.

What is a Complex Element?

A complex element is an XML element that contains other elements and/or attributes.

There are four kinds of complex elements:

• empty elements
• elements that contain only other elements
• elements that contain only text
• elements that contain both other elements and text

Note: Each of these elements may contain attributes as well!

Examples of Complex XML Elements

A complex XML element, "product", which is empty:

<product pid="1345"/>

A complex XML element, "employee", which contains only other elements:

<employee>
<firstname>John</firstname>
<lastname>Smith</lastname>
</employee>

A complex XML element, "food", which contains only text:

<food type="dessert">Ice cream</food>

A complex XML element, "description", which contains both elements and text:

<description>
It happened on <date lang="norwegian">03.03.99</date> ....
</description>

How to Define a Complex Element

Look at this complex XML element, "employee", which contains only other elements:

<employee>
<firstname>John</firstname>
<lastname>Smith</lastname>
</employee>

We can define a complex element in an XML Schema in different ways:.

1. The "employee" element can be declared directly by naming the element, like this:

<xs:element name="employee">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="firstname" type="xs:string"/>
      <xs:element name="lastname" type="xs:string"/>
    </xs:sequence>
  </xs:complexType>
</xs:element>

If you use the method described above, only the "employee" element can use the specified complex type. Notice that the child elements, "firstname" and "lastname", are surrounded by the <sequence> indicator. This means that the child elements must appear in the same order as they are declared; "firstname" first and "lastname" second. You will learn more about indicators in the XSD Indicators chapter.

2. The "employee" element can have a type attribute that references to the name of the complex type to use:

<xs:element name="employee" type="personinfo"/>

<xs:complexType name="personinfo">
  <xs:sequence>
    <xs:element name="firstname" type="xs:string"/>
    <xs:element name="lastname" type="xs:string"/>
  </xs:sequence>
</xs:complexType>

If you use the method described above, several elements can refer to the same complex type, like this:

<xs:element name="employee" type="personinfo"/>
<xs:element name="student" type="personinfo"/>
<xs:element name="member" type="personinfo"/>

<xs:complexType name="personinfo">
  <xs:sequence>
    <xs:element name="firstname" type="xs:string"/>
    <xs:element name="lastname" type="xs:string"/>
  </xs:sequence>
</xs:complexType>

You can also base a complex type element on an existing complex type and add some elements, like this:

<xs:element name="employee" type="fullpersoninfo"/>

<xs:complexType name="personinfo">
  <xs:sequence>
    <xs:element name="firstname" type="xs:string"/>
    <xs:element name="lastname" type="xs:string"/>
  </xs:sequence>
</xs:complexType>

<xs:complexType name="fullpersoninfo">
  <xs:complexContent>
    <xs:extension base="personinfo">
      <xs:sequence>
        <xs:element name="address" type="xs:string"/>
        <xs:element name="city" type="xs:string"/>
        <xs:element name="country" type="xs:string"/>
      </xs:sequence>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>

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