Declaring Complex Elements with Sub Elements Only

This section describes a tutorial example on how to declare an element that accepts only sub (child) elements without attributes and text content using a user define complexType datatype.

A complex element with sub elements only is an element with sub (child) elements, but no text content and no attribute. This type of element can be declared with a "complexType" datatype with "complexContent" containing some "element"s.

A good example of complex elements with attributes only is the <ul> element in HTML documents. It accepts only sub element of <li>. But it should not have any text content, or any attributes.

Rule 1. The "complexType" component defines a datatype for a complex element.

Rule 2. The "complexContent" component used inside "complexType" specifies that the complex element could have sub (child) elements and attributes.

Rule 3. The "restriction" component inside "complexContent" restricts the specified base datatype for the content to be more restrictive.

Rule 4. When the built-in datatype "anyType" is used as the base datatype of a "restriction" component inside "complexContent", it provides an empty datatype definition.

Rule 5. The "sequence" component inside "restriction" defines a sequence model group, which can be used to specify a list of sub elements.

Putting all these rules together, I wrote this sample schema, complexType_sub_element_only.xsd, that defines <ul> to accept only sub elements:

<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- complexType_sub_element_only.xsd
 - Copyright (c) 2013, HerongYang.com, All Rights Reserved.
-->

 <xs:element name="ul">
 <xs:complexType>
  <xs:complexContent>
   <xs:restriction base="xs:anyType">
    <xs:sequence>
    <xs:element name="li" type="xs:string" maxOccurs="unbounded"/>
    </xs:sequence>
   </xs:restriction>
  </xs:complexContent>
 </xs:complexType>
 </xs:element>

</xs:schema>

Let's try this schema on a sample XML document, complexType_sub_element_only.xml, with some errors:

>type complexType_sub_element_only.xml

<?xml version="1.0"?>
<ul note="Key Words">
 <li>XSD</li>
 <li>Tutorial</li>
 Example
</ul>


>java XsdSchemaValidator complexType_sub_element_only.xsd 
complexType_sub_element_only.xml

Error:
   Line number: 2
   Column number: 22
   Message: cvc-complex-type.3.2.2: Attribute 'note' is not allowed
   to appear in element 'ul'.

Error:
   Line number: 6
   Column number: 6
   Message: cvc-complex-type.2.3: Element 'ul' cannot have 
   character [children], because the type's content type is 
   element-only.

Failed with errors: 2

Last update: 2013.

Table of Contents

 About This Book

 Introduction to XML Schema

 XML Editor and Schema Processor - XMLPad

 Java API for XML Processing - JAXP

 JAXP - XML Schema (XSD) Validation

 Xerces2 Java Parser - Java API of XML Parsers

 Using Xerces2 Java API

 XML Schema Language - Basics

 Introduction of XSD Built-in Datatypes

 "string" and Its Derived Datatypes

 "decimal" and Its Derived Datatypes

 "dateTime" and Its Related Datatypes

 Miscellaneous Built-in Datatypes

 Facets, Constraining Facets and Restriction Datatypes

 "simpleType" - Defining Your Own Simple Datatypes

Complex Element Declaration

 Complex Element vs. Simple Element

 Declaring Empty Elements

 Declaring Simple Elements

 Declaring Complex Elements with Simple Content

 Declaring Complex Elements with Attributes Only

Declaring Complex Elements with Sub Elements Only

 Declaring Complex Elements with Attributes and Sub Elements

 Declaring Complex Elements with Attributes, Sub Elements & Text Content

 Using Shorthand for "complexContent" with "restriction"

 Identity-Constraints: unique, key and keyref

 Assertion as Custom Validation Rules

 XML Schema Location and Namespace in XML Documents

 Overriding Element Types in XML Documents

 Linking Multiple Schema Documents Together

 Glossary

 References

 PDF Printing Version