Recursive definition of XML Element

Is recursive definition of XML elements allowed? I have a need for a
recursive xml element like this:

	<Node process="T">
		<Node process="S">
			<Node process="C1">
				<Node process="C2">
					<Node process="P1"/>
					<Node process="P2"/>
					<Node process="P3"/>
				</Node>
				<Node process="C3">
					<Node process="P4"/>
					<Node process="P5"/>
					<Node process="P6"/>
				</Node>
			</Node>
		</Node>
		<Node process="Y1"/>
	</Node>

My corresponding schema file (.xsd) is like:

	<xs:complexType name="NodeType">
		<xs:sequence minOccurs="0" maxOccurs="unbounded">
			<xs:choice>
				<xs:element name="Node" type="NodeType"/>
				<xs:element name="NodeRef">
					<xs:complexType>
						<xs:attribute name="name"
type="xs:string" use="optional"/>
						<xs:attribute name="node"
type="xs:string" use="required"/>
					</xs:complexType>
				</xs:element>
				<xs:element name="Cluster">
					<xs:complexType>
						<xs:sequence
maxOccurs="unbounded">
							<xs:element
name="Node" type="NodeType"/>
						</xs:sequence>
						<xs:attribute name="name"
type="xs:string" use="required"/>
					</xs:complexType>
				</xs:element>
			</xs:choice>
		</xs:sequence>
		<xs:attribute name="name" type="xs:string"/>
		<xs:attribute name="process" type="xs:string"/>
	</xs:complexType>

The xml file itself can be parsed, but when parsed together with xsd
validation(using xerces/xalan), the following error happens:
"The attribute 'process' is already used in element 'Node'."

Any idea? Is the above XML valid, or is this a bug/defect of Apache parser?
If the XML is invalid, could you suggest an alternative?

Thanks,

Yanrui

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