XSLT, 2nd Edition

Creating Union Types

A union type references two or more datatypes. The valid content of a union type is a value from one of those datatypes. We’ll create another schema that defines a list of zipcodes, then create a union type that allows the states attribute to be either a list of state abbreviations or a list of zipcodes. Here’s an excerpt from the schema:

<?xml version="1.0" encoding="UTF-8"?>
<!-- union.xsd -->
...
  <xs:simpleType name="zipcode">
    <xs:restriction base="xs:integer">
      <xs:pattern value="[0-9]{5}"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="zipcode-list-type">
    <xs:list itemType="zipcode"/>
  </xs:simpleType>

  <xs:simpleType name="state-abbr-type">
    <xs:restriction base="xs:string">
      <xs:length value="2"/>
    </xs:restriction>
  </xs:simpleType>

  <xs:simpleType name="state-abbr-list-type">
    <xs:list itemType="state-abbr-type"/>
  </xs:simpleType>

  <xs:simpleType name="address-union-type">
    <xs:union memberTypes="state-abbr-list-type zipcode-list-type"/>
  </xs:simpleType>
  ...
  <xs:element name="priorAddresses">
    <xs:complexType>
      <xs:attribute name="states" type="address-union-type"/>
    </xs:complexType>
  </xs:element>

</xs:schema>

And here’s a valid document for this schema:

<?xml version="1.0" encoding="utf-8"?>
<!-- union.xml -->
<person
  xmlns="http://www.oreilly.com/xslt"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.oreilly.com/xslt union.xsd">
  <name>Doug Tidwell</name>
  <birthday>1965-06-19</birthday>
  <age>42</age>
 <priorAddresses ...