Question

I want to declare an element to be included in a complex type declaration, and the element has a mandatory attribute: “option=MyOption”, but the value of the “option” attribute could be anything, depending on the context.

That is: the attribute “option” with some unknown value should be mandatory in any document using the complex type containing this element.

Example:

    <xs:element name="SpecialOption" type="xs:string"/>

    <xs:complexType name="SpecialOptions">
        <xs:sequence>
            <xs:element ref="SpecialOption" minOccurs="1" maxOccurs="100"/>
            <xs:element ref="XXX"/>     
        </xs:sequence>
    </xs:complexType>   

In this case the “SpecialOption” element in the complex type “SpecialOptions” should have this mandatory attribute.

I don’t know how to declare a mandatory attribute for an element in XSD, or how to specify that the attribute must have a value that is not yet known.

Answer 1

You need to modify the definition of the “SpecialOption” element to include the required attribute. Update this code:

<xs:element name="SpecialOption" type="xs:string"/>

to this:

<xs:element name="SpecialOption">
  <xs:complexType>
    <xs:simpleContent>
      <xs:extension base="xs:string">
        <xs:attribute name="Option" type="xs:string" use="required"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
</xs:element>

With this change your complex type will contain the required “Option” attribute on all instances of the “SpecialOption” element in the “SpecialOptions” complex type. Declaring the “Option” attribute to be of type xs:string will allow any value to be passed in this field.