This section describes a tutorial example on how to declare an element that accepts only attributes using a user defined complexType datatype.
A complex element with attributes only is an element with no text content and no sub (child) element. What it has
is only attributes.
This type of element can be declared with a "complexType" datatype with "complexContent" containing some "attribute"s.
A good example of complex elements with attributes only is the <img> element in HTML documents.
It accepts only attributes like "src", and "alt". But it should not accept any sub elements or any text content.
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. Each "attribute" component inside "restriction" defines an additional attribute for the base datatype.
Putting all these rules together, I wrote this sample schema, complexType_attribute_only.xsd,
that defines <img> to accept only 2 attributes:
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- complexType_attribute_only.xsd
- Copyright (c) 2007 by Dr. Herong Yang. All rights reserved.
-->
<xs:element name="img">
<xs:complexType>
<xs:complexContent>
<xs:restriction base="xs:anyType">
<xs:attribute name="src" type="xs:string"/>
<xs:attribute name="alt" type="xs:string"/>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
</xs:element>
</xs:schema>
Let's try this schema on a sample XML document, complexType_simpleContent.xml, with some errors:
>type complexType_attribute_only.xml
<?xml version="1.0"?>
<img src="picture.jpg" alt="Picture"><b>Nice</b> Picture!</img>
>java XsdSchemaValidator complexType_attribute_only.xsd
complexType_attribute_only.xml
Error:
Line number: 2
Column number: 64
Message: cvc-complex-type.2.1: Element 'img' must have no
character or element information item [children], because the
type's content type is empty.
Failed with errors: 1
