Question

I’m using XmlReader to validate Xml against Xsd.

When I validate this xml

<?xml version="1.0" encoding="utf-8" ?>
<A><B>sdf</B></A>

against this schema:

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

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

<xs:element name="A">
    <xs:complexType>
        <xs:sequence>
            <xs:element ref="B"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

</xs:schema>

validation is OK.

But if I add namespace:

<?xml version="1.0" encoding="utf-8" ?>
<A xmlns="myns"><B>sdf</B></A>

and corresponding schema:

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

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

<xs:element name="A">
    <xs:complexType>
        <xs:sequence>
            <xs:element ref="B"/>
        </xs:sequence>
    </xs:complexType>
</xs:element>

</xs:schema>

I accept System.Xml.Schema.XmlSchemaValidationException: The ‘B’ element is not declared.
Why this happens? And how can I add a namespace?

Answer 1

The reason you are getting the validation error is that your schema is actually two schemas. You have two root elements, A and B. A root element cannot be implicitly used as a type. You need to tell XSD that you want to use types from another schema (using an import), or make those types local to the schema (using a complexType definition).

Example: extract B out into it’s own schema. It cannot share the same namespace:

<?xml version="1.0" encoding="utf-8"?>
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="myns2">
  <xs:element name="B" type="xs:string" />
</xs:schema>

Then you can reference B from your A type by using import:

<?xml version="1.0" encoding="utf-8"?>
<xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="myns" xmlns:myns2="myns2">

  <xs:import namespace="myns2" />

  <xs:element name="A">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="myns2:B" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

This allows you to have the following valid XML instance:

<?xml version="1.0" encoding="utf-8" ?>
<A xmlns="myns">
  <B xmlns="myns2">sdf</B>
</A>

The reason you were able to validate the non-namespace’d versions of the types was because in order to be valid XML two things need to be true:

• Well formed XML
• Must conform to any referenced schema types

In the non-namespace’d XML file, there is by definition no reference to any schema types, so therefore the document is valid XML.