Question

I am trying to develop an XSD for some XML that looks roughly like this:

<root>
  <thing id="1"/>
  <thing id="2"/>
  <thing id="3">
    <subelement>
      ...
    </subelement>
  </thing>
</root>

Where a thing of each id is required once, and the thing with the id of “3” requires specific subelements.

I was able to create the requirement of one thing of each ID by creating a abstract complex type and extending off of that (though it’s still untested),

<xs:element name="thing" type="tns:abstractType" minOccurs="3" maxOccurs="3">
  <xs:unique name="EachIdRequired">
    <xs:selector xpath="thing" />
    <xs:field xpath="@id"/>
  </xs:unique>
</xs:element>

<xs:complexType name="abstractType" abstract="true/>
<xs:complexType name="idOne">
  <xs:complexContent>
    <xs:extension base="tns:abstractType">
      <xs:attribute name="id" fixed="1" type="xs:integer" use="required"/>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>
<xs:complexType name="idTwo">
  <xs:complexContent>
    <xs:extension base="tns:abstractType">
      <xs:attribute name="id" fixed="2" type="xs:integer" use="required"/>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>
<xs:complexType name="idThree">
  <xs:complexContent>
    <xs:extension base="tns:abstractType">
      <xs:attribute name="id" fixed="3" type="xs:integer" use="required"/>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>

However, I am unsure how to also have the requirement of the complexType of id 3 to also have the required subelements. The only way I have seen an element defined with both an attribute and subelements is the use of an extension, however idThree is already extending the abstract type.

Is what I am going for possible in some other way? I am doubtful but I want to be sure. XSD seems somewhat limiting.

Answer 1

Not possible in XML Schema. The best Schema langage for such a structure is Relax NG. See http://relaxng.org/