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XSD Complex Elements

How to define and use XML Schema (XSD) complex elements that contain other elements, text, or attributes, including direct declaration and type referencing.

An XML 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.

Complex elements can be of four types:

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

Examples of Complex Elements

A complex XML element, called "book":

<book author="Tom Nolan"/>

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

<book>
	<title>A Great Book</title>
	<author>Tom Nolan</author>
	<publisher>Tutorial Reference</publisher>
</book>

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

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

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

<description>  
I was born in <date lang="norwegian">01.02.99</date> ....  
</description>

How to Define a Complex Element

Consider the "book" XML element, which contains only other elements:

<book>
	<title>A Great Book</title>
	<author>Tom Nolan</author>
	<publisher>Tutorial Reference</publisher>
</book>

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

1. Declare directly by naming the element

<xs:element name="book">
	<xs:complexType>
		<xs:sequence>
			<xs:element name="title"  type="xs:string"/>
			<xs:element name="author"  type="xs:string"/>
			<xs:element name="publisher"  type="xs:string"/>
		</xs:sequence>
	</xs:complexType>
</xs:element>

In this way, only "book" element can use the specified complex type.

2. Declare with type attribute that referees to the name of the complex type to use

<xs:element name="book" type="bookinfo"/>

<xs:complexType name="bookinfo">
	<xs:sequence>
		<xs:element name="title"  type="xs:string"/>
		<xs:element name="author"  type="xs:string"/>
		<xs:element name="publisher"  type="xs:string"/>
	</xs:sequence>
</xs:complexType>

In this way, you can have several element that can refer to the same complex type. For example:

<xs:element name="book" type="bookinfo"/>
<xs:element name="teacherbook" type="bookinfo"/>
<xs:element name="studentbook" type="bookinfo"/>

<xs:complexType name="bookinfo">
	<xs:sequence>
		<xs:element name="title"  type="xs:string"/>
		<xs:element name="author"  type="xs:string"/>
		<xs:element name="publisher"  type="xs:string"/>
	</xs:sequence>
</xs:complexType>

Furthermore, you can base a complex type on an existing complex type and add some elements:

<xs:element name="book" type="enanchedbookinfo"/>

<xs:complexType name="bookinfo">
	<xs:sequence>
		<xs:element name="title"  type="xs:string"/>
		<xs:element name="author"  type="xs:string"/>
		<xs:element name="publisher"  type="xs:string"/>
	</xs:sequence>
</xs:complexType>

<xs:complexType name="enanchedbookinfo">  
	<xs:complexContent>
		<xs:extension base="personinfo">
			<xs:sequence>
			<xs:element name="publishdate"  type="xs:date"/>
			<xs:element name="country"  type="xs:string"/>
			<xs:element name="price"  type="xs:decimal"/>
			</xs:sequence>
		</xs:extension>
	</xs:complexContent>
</xs:complexType>
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