I think you can do this by using a simpleType to define a short string and
then a complexType of simpleContent extending the short string with an
attribute.
Like this:
<xs:element name="ADDRESS" type="ShortAddress"/>
<xs:complexType name="ShortAddress">
<xs:simpleContent>
<xs:extension base="shortString">
<xs:attribute name="type" type="xs:string"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:simpleType name="shortString">
<xs:restriction base="xs:string">
<xs:minLength value="1" />
<xs:maxLength value="50" />
</xs:restriction>
</xs:simpleType>
Regards,
John