XMLSchema - Element refers to itself - how to do it? - reference

Question

I have a task where I need to create an element "Worker" which has 0 or more subelements "subordinate". I have to use key and keyref to create the references. I can't figure out how make the references "work". Here's what I've written so far:
<xsd:element name="Workers">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="Worker" maxOccurs="unbounded">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="subordinate" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:attribute name="identyfikator" type="PESEL" use="required"/>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
<xsd:key name="id">
<xsd:selector xpath="Worker"/>
<xsd:field xpath="#identyfikator"/>
</xsd:key>
<xsd:keyref name="subordinate_ref" refer="id">
<xsd:selector xpath="Worker/subordinate"/>
<xsd:field xpath="#identyfikator"/>
</xsd:keyref>
</xsd:element>
PESEL is my own type and the key restriction works well as I am unable to create two workers with the same key in XML document. However, I can create anything as "subordinate" element and no warnings will be displayed. As I understand, in case of such reference I should be only able to add workers as subordinates if they already exist, right? How do I create proper reference?
This is my first time working with XMLSchema so sorry if the code is messy.
Thanks in advance!

Answer 1

Make a Worker ComplexType and have Worker and Subordinate both be of that type.
Approximately like so:
<!-- Define the below where appropriate. -->
<xsd:element name="Worker" type="WorkerType" />
<xsd:complexType name="WorkerType">
<xsd:sequence>
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="subordinate" type="WorkerType" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:attribute name="identyfikator" type="PESEL" use="required"/>
</xsd:complexType>
Also, if you want items to have a unique id, then consider using (or extending) the xsd:ID datatype. This gives you free uniqueness and referential checks using xsd:IDREF.
<xsd:attribute name="identyfikator" type="xsd:ID" use="required"/>