<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

	<xsd:simpleType name="myDecimal">

		<xsd:restriction base="xsd:decimal">			

			<xsd:totalDigits value="18"/>			

		</xsd:restriction>

	</xsd:simpleType>

	<xsd:element name="foo">

		<xsd:complexType>

			<xsd:sequence>

				<xsd:element name="val" type="myDecimal" maxOccurs="unbounded"/>

				<xsd:element name="ref" type="myDecimal" minOccurs="0"/>

			</xsd:sequence>

		</xsd:complexType>

			<xsd:selector xpath="val"/>

			<xsd:field xpath="."/>

		</xsd:key>

		<xsd:keyref name="myKeyRef" refer="myKey">

			<xsd:selector xpath="ref"/>

			<xsd:field xpath="."/>

		</xsd:keyref-->

	</xsd:element>

</xsd:schema>