Xml Schema: Extending base root element with unique/key/keyref element.

**icesign** · Aug 4 '09, 09:55 AM

I know that the selector of these elements has a scope relative to the element being declared, but maybe there is a way to get beyond bounds of this scope or maybe just a way to extend base element?
Here’s a working example:

Code:

<xs:schema id="schema"
    targetNamespace="http://tempuri.org/schema.xsd"
    elementFormDefault="qualified"
    xmlns="http://tempuri.org/schema.xsd"
    xmlns:mstns="http://tempuri.org/schema.xsd"
    xmlns:xs="http://www.w3.org/2001/XMLSchema">
	
	<xs:element name="element" abstract="true" type="TElement"/>
	<xs:element name="local" type="TLocal" substitutionGroup="element"/>

	<xs:element name="root" type="TRoot">
		<!--declaring constraint within TRoot (root element of any document)-->
		<xs:unique name="local-name-constraint">
			<xs:selector xpath=".//mstns:local"/>
			<xs:field xpath="@name"/>
		</xs:unique>
	</xs:element>

	<xs:complexType name="TElement" abstract="true">
	</xs:complexType>

	<xs:complexType name="TRoot">
		<xs:complexContent>
			<xs:extension base="TElement">
				<xs:sequence>
					<xs:element ref="element" maxOccurs="unbounded"/>
				</xs:sequence>
			</xs:extension>
		</xs:complexContent>
	</xs:complexType>

	<xs:complexType name="TLocal">
		<xs:complexContent>
			<xs:extension base="TElement">
				<xs:sequence>
					<xs:element ref="element" minOccurs="0" maxOccurs="unbounded"/>
				</xs:sequence>
				<xs:attribute name="name" use="required" type="xs:string"/>
			</xs:extension>
		</xs:complexContent>
	</xs:complexType>
</xs:schema>

…and XML document

Code:

<root xmlns="http://tempuri.org/schema.xsd">
	<local name="a"/>
	<local name="b">
		<local name="a"/>
	</local>
</root>

It works and I’ve got notified that there is a duplicate key sequence. But what if I have an extension to this schema where I declared another element:

Code:

<root xmlns="http://tempuri.org/schema.xsd"
	  xmlns:e="http://tempuri.org/ext.xsd">
	<local name="one">
		<e:extended key="next"/>
	</local>
	<local name="two">
		<local name="one"/>
		<e:extended key="next"/>
	</local>
</root>

Code:

<xs:schema id="ext"
    targetNamespace="http://tempuri.org/ext.xsd"
    elementFormDefault="qualified"
    xmlns="http://tempuri.org/ext.xsd"
    xmlns:mstns="http://tempuri.org/ext.xsd"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
	xmlns:base="http://tempuri.org/schema.xsd"
>

	<xs:import namespace="http://tempuri.org/schema.xsd"
			   schemaLocation="schema.xsd"/>

	<xs:element name="extended" type="TExtended" substitutionGroup="base:element">
		<xs:unique name="extended-key-constraint">
			<xs:selector xpath="I can't get to the root of the document here"/>
			<xs:field xpath="@key"/>
		</xs:unique>
	</xs:element>
	
	<xs:complexType name="TExtended">
		<xs:complexContent>
			<xs:extension base="base:TElement">
				<xs:sequence>
					<xs:element ref="base:element" minOccurs="0" maxOccurs="unbounded"/>
				</xs:sequence>
				<xs:attribute name="key" use="required" type="xs:string"/>
			</xs:extension>
		</xs:complexContent>
	</xs:complexType>

</xs:schema>

How can I set uniqueness to the element from the schema extensions?