Question

The XML I’m trying to validate is as follows:

<root>     <element attribute='foo'>         <bar/>     </element>     <element attribute='hello'>         <world/>     </element> </root> 

How can this be validated using a Schema?

Note:

element can only contain bar when attribute=’foo’.

element can only contain world when attribute=’hello’

Answer 1

You can’t do this in XML Schema 1.0. In XML Schema 1.1 you will be able to use the <xs:assert> element to do it, but I’m guessing you want something that you can use now.

You can use Schematron as a second layer of validation that will allow you to test arbitrary XPath assertions about your XML document. There’s a fairly old article about embedding Schematron in XSD that you might find helpful.

You’d do something like:

<rule context='element'>   <report test='@attribute = 'foo' and *[not(self::bar)]'>     This element's attribute is 'foo' but it holds an element that isn't a bar.   </report>   <report test='@attribute = 'hello' and *[not(self::world)]'>     This element's attribute is 'hello' but it holds an element that isn't a world.   </report> </rule> 

Or of course you can switch to RELAX NG, which does this in its sleep:

<element name='element'>   <choice>     <group>       <attribute name='attribute'><value>foo</value></attribute>       <element name='bar'><empty /></element>     </group>     <group>       <attribute name='attribute'><value>hello</value></attribute>       <element name='world'><empty /></element>     </group>   </choice> </element>