How to fix an XSD validation error?

Question

Hi, I have an XML form with an element 0, which is well-formed but not valid. When I try to validate it XMLSpy I get a following error: Nothing is allowed inside empty element 'hidden'. Below is my schema:

<xs:element name="hidden">
    <xs:complexType>
     <xs:attribute name="datatype" type="xs:string" use="optional"/>
     <xs:attribute name="alias" type="xs:string" use="optional"/>
     <xs:attribute name="source" type="xs:string" use="optional"/>
     <xs:attribute name="name" type="xs:string" use="required"/>
     <xs:attribute name="lookup" type="xs:string" use="optional"/>
    </xs:complexType>
</xs:element>

What do I need to add to the above schema to fix this error? Thanx ml

Answer 1

Your "hidden" element is defined as being empty since you don't have anything in the schema explicitly allowing child elements. I'm assuming you're wanting something like

<hidden *[attributes]*>
   <some_other_element/>
</hidden>

But according to http://www.w3schools.com/Schema/schema_complex_empty.asp you have implicitly defined "hidden" to be empty. You need to define which elements can appear inside "hidden". There are many ways to do this and I suggest starting by reading http://www.w3schools.com/Schema/schema_complex.asp.

Answer 2

Thank you Michael and welbog. Unfortunately, I have tried your suggestions and cannot get it right. 0 still throws an error.

Answer 3

As welbog noted, you defined a complex empty element. Assuming you want only text within the hidden tag, you could write a schema along theses lines :

<xs:element name="hidden">
  <xs:complexType>
    <xs:simpleContent>
      <xs:extension base="xs:integer">
        <xs:attribute name="datatype" type="xs:string" use="optional"/>
        <xs:attribute name="alias"    type="xs:string" use="optional"/>
        <xs:attribute name="source"   type="xs:string" use="optional"/>
        <xs:attribute name="name"     type="xs:string" use="required"/>
        <xs:attribute name="lookup"   type="xs:string" use="optional"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
</xs:element>

This way, you can have a piece of XML like this one:

<hidden datatype="foo" name="bar">0</hidden>

What is going on here is that I defined "hidden" to be an extension of xs:integer (by the way, you can make it extends any type you want), which means that "hidden" elements are like integers element, but with additional constraints, or in this case with additional attributes.