I am trying to define a simple schema that contains a “circular” reference and need some advice. I think this is a fairly standard situation.
I have a list of users who belong to user groups. So I envision two doc-types in my schema - user and user-group. A user may belong to many user-groups and a user-group contains many users. How would I define my schema?

Here is a sample schema that I would have thought should work. Tamino won’t let me define this because of the ordering (“missing node reference” error) but there is no way to fix this. What to do?

Schema:
<?xml version = "1.0" encoding = "US-ASCII"?>
<xs:schema xmlns:xs = “XML Schema” xmlns:tsd = “http://namespaces.softwareag.com/tamino/TaminoSchemaDefinition”>
xs:annotation
xs:appinfo
<tsd:schemaInfo name = “test”>
<tsd:doctype name = “user-group-role”>
tsd:logical
tsd:contentclosed</tsd:content>
</tsd:logical>
</tsd:doctype>
<tsd:doctype name = “user”>
tsd:logical
tsd:contentclosed</tsd:content>
</tsd:logical>
</tsd:doctype>
<xs:element name = “user”>
xs:complexType
xs:sequence
<xs:element name = “user-group-role_obj_id” type = “xs:string” minOccurs = “0” maxOccurs = “unbounded”>
xs:annotation
xs:appinfo
tsd:elementInfo
tsd:physical
tsd:native
tsd:objectRef
tsd:dereference</tsd:dereference>
<tsd:accessPredicate operator = “=”>
tsd:nodeRef/user-group-role/@ID</tsd:nodeRef>
</tsd:accessPredicate>
</tsd:objectRef>
</tsd:native>
</tsd:physical>
</tsd:elementInfo>
</xs:appinfo>
</xs:annotation>
</xs:element>
</xs:sequence>
<xs:attribute name = “userid” type = “xs:string”></xs:attribute>
<xs:attribute name = “password” type = “xs:string”></xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name = “user-group-role”>
xs:complexType
xs:sequence
<xs:element name = “user_obj_id” type = “xs:string” minOccurs = “0” maxOccurs = “unbounded”>
xs:annotation
xs:appinfo
tsd:elementInfo
tsd:physical
tsd:native
tsd:objectRef
tsd:dereference</tsd:dereference>
<tsd:accessPredicate operator = “=”>
tsd:nodeRef/user/@ID</tsd:nodeRef>
</tsd:accessPredicate>
</tsd:objectRef>
</tsd:native>
</tsd:physical>
</tsd:elementInfo>
</xs:appinfo>
</xs:annotation>
</xs:element>
</xs:sequence>
<xs:attribute name = “group_name” type = “xs:string”></xs:attribute>
</xs:complexType>
</xs:element>

Tamino’s schema does not allow to reference a doctype not yet fully being defined. Hence, it is not possible to define a schema with a cycle of doctypes referring each other in one step. Instead you have to define a restricted schema in the first step containing just the backward reference and the forward reference being removed:

…
<xs:element name=“user-group-role”>
xs:complexType
xs:sequence
<xs:element name=“user_obj_id” type=“xs:string” minOccurs=“0” maxOccurs=“unbounded”>
xs:annotation
xs:appinfo
tsd:elementInfo
tsd:physical
tsd:native

</tsd:native>
</tsd:physical>
</tsd:elementInfo>
</xs:appinfo>
</xs:annotation>
</xs:element>
</xs:sequence>
<xs:attribute name=“group_name” type=“xs:string”/>
</xs:complexType>
</xs:element>

After defining this schema successfully, you should be able to define your original schema.

Ulrich, thanks for this. Sorry it took so long to acknowledge your help.

I guess this means that if I want to have this kind of thing in my schema I have to keep multiple .TSD files around in order to recreate my schema. Ugh.

Do you have any comments on my approach? Perhaps I should just use my own keys and implement my own “foreign key” checking? I have received that advice from one other person already but I am interested in your thoughts.