Question

I have an XSD of this form:

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://www.example.org/example"
    xmlns:tns="http://www.example.org/example" elementFormDefault="qualified">

    <complexType name="bType">
    </complexType>

    <complexType name="aType">
        <choice maxOccurs="unbounded">
            <element name="a" type="tns:aType" />
            <element name="b" type="tns:bType" />
        </choice>
    </complexType>

    <element name="topelement">
        <complexType>
            <sequence>
                <element name="a" type="tns:aType" maxOccurs="1" />
            </sequence>
        </complexType>
    </element>
</schema>

And an XML file that I expect to match it, e.g:

<?xml version="1.0" encoding="UTF-8"?>
<topelement xmlns="http://www.example.org/example"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.example.org/example example.xsd ">
  <a> <!-- Error on this line. -->
    <a/>
    <b/>
    <b/>
    <a/>
  </a>
</topelement>

Unfortunately the XSD says that this is not valid with the following error:

cvc-complex-type.2.4.b: The content of element 'a' is not complete. One of '{"http://www.example.org/example":a, "http://www.example.org/example":b}' is expected.  example.xml line 5

As far as I can tell, I’ve done everything I need to do for the tag to be complete. I’ve filled it with an unbounded choice of ‘a’ and ‘b’ tags. Can anyone see what’s gone wrong?

To clarify, I want there to be only one ‘a’ tag under topelement, and underneath that, a mix of ‘a’ and ‘b’ tags.

Answer 1

Worked it out… The error is misleading because it’s complaining about the wrong ‘a’.

Rename the top-level ‘a’ to ‘c’ and it still complains about ‘a’ on line 5.

The fix is to add minOccurs=0 to the choice element so that not all ‘a’ elements need children.