Recursive element definition

Hi there,
I trying to solve the following problem:
I want define a elemet CATEGORY.
As a category can contain sub-categories the element itself is used again as
"child"-element in the "parent"-element.
I tried the following Schema-definition. But is looks somehow strange to me:
<xsd:element name="CATEGORY">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="CATEGORY">
<xsd:element ref="PART"/>
</xsd:sequence>
<xsd:attribute name="NAME" type="xsd:string" use="required"/>
<xsd:attribute name="SEQ" type="xsd:integer" use="required"/>
</xsd:complexType>
</xsd:element>

Can anyone verify that or has a tip for me ?
Thx.
Stefan