I’m trying to use a XSD document to detect the uniqueness of a combination of attributes from two elements.

I’ve added the following unique statement to my XSD:

<xs:unique name="uniqueEMNameParentID">
    <xs:selector xpath=".//EM"/>
    <xs:field xpath="@Name"/>
    <xs:field xpath=".//Station/@ID"/>
</xs:unique>

And this is an example of my XML:

<?xml version="1.0" encoding="utf-8"?>
<Project>
  <PLC Name="PLC">
    <Type>
      <TypeDef ID="1" Name="G05" Description="" />
    </Type>
    <SA ID="01">
      <Station ID="100">
        <EM ID="01" Name="IR01" IsRobot="TRUE">          
        </EM>
      </Station>
    </SA>
    <SA ID="02">
      <Station ID="100">
        <EM ID="02" Name="IR01" IsRobot="TRUE">
        </EM>
        <EM ID="03" Name="IR03" IsRobot="TRUE">      
        </EM>
      </Station>
    </SA>
  </PLC>
</Project>

When using notepad++ the XSD gives me the correct error: IR01 is a duplicate key for unique identity constraint ‘uniqueEMNameParentID’. When using this same XSD in C# it thinks my document is okay. This is my C# code:

 private void ValidateXML()
 {
     XmlSchemaSet schema = new XmlSchemaSet();
     schema.Add("", @"Z:VMshareMaartenWindowsFormsApplication3WindowsFormsApplication3XMLXSDScheme3.xsd");
     projectXML.Schemas.Add(schema);

     projectXML.Validate((object sender, System.Xml.Schema.ValidationEventArgs args) =>
     {
         MessageBox.Show(args.Message);
     });
 }

My XML Document does not contain any namespaces, my XSD does not contain a targetnamespace and both attribute and elementformdefault are set to unqualified. Does anyone have any idea what it could be?