Hi,
I'm having the following problem with XSD authoring.

I want to have a type that includes an element.
Then, I want to inherit from that type, and force the element inside it to be of more specific type.

As I understand, this can be done using restriction derivation, but only if the specific element inside the deriving type is a restriction of the original element.
Is there any idea how to derive from the original type and make the element in the deriving type an extesion of the element in the parent type?

Here is an example, that shows what I want to achieve, but returns error on XMLSpy:
<?xml version="1.0" encoding="UTF-8"?>
<!-- edited with XMLSpy v2011 rel. 3 sp1 (http://www.altova.com) by Asi (Comm-IT) -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:complexType name="Covariance">
<xs:sequence>
<xs:element name="x" type="xs:double"/>
<xs:element name="y" type="xs:double"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="ExtendedCovariance">
<xs:complexContent>
<xs:extension base="Covariance">
<xs:sequence>
<xs:element name="z" type="xs:double"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="Detection">
<xs:sequence>
<xs:element name="someElement" type="xs:string"/>
<xs:element name="covariance" type="Covariance"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="RestrictedDetection">
<xs:complexContent>
<xs:restriction base="Detection">
<xs:sequence>
<xs:element name="someElement" type="xs:string"/>
<xs:element name="covariance" type="ExtendedCovariance"/>
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>
</xs:schema>

The error message:
Type RestrictedDetection (>def) is not a valid restriction of type Detection (>def).

Does anyone have any idea how can I achive my goal?