ht@i... (Henry S. Thompson) wrote in message news:<f5bpt41iezn.fsf@e...>...
> <xsd:redefine schemaLocation="schema1.xsd">
>   <xsd:group name="INSURANCESVCRQMSGS">
>    <xsd:choice>
>     <xsd:group ref="INSURANCESVCRQMSGS">
>     <xsd:element ref="MyAdditionalElement" minOccurs="1" maxOccurs="1"/>
>    </xsd:choice>
>   </xsd:group>
>  </xsd:redefine>
> 
> Hope this helps
> 
> ht

Thanks for your reply, Henry, but I had a problem with this syntax.

XMLSpy thinks that this syntax creates an unacceptable circular
reference.  I went to the W3C XML tutorial
(http://www.w3c.org/TR/xmlschema-1), did a search on 'circular', and
came up with the following:

"3.8.6 Constraints on Model Group Schema Components
All model groups (see Model Groups (§3.8)) must satisfy the following
constraints.

Schema Component Constraint: Model Group Correct 

All of the following must be true:
1) The values of the properties of a model group must be as described
in the property tableau in The Model Group Schema Component (§3.8.1),
modulo the impact of Missing Sub-components (§5.3).
2) Circular groups are disallowed. That is, within the {particles} of
a group there must not be at any depth a particle whose {term} is the
group itself."

Number two seems to say that you can't have a reference to the same
group for Model Groups, even within a redefine tag.  However, the
information on Attribute Groups is different, and provides an
allowance for circular references inside of a redefine tag:

"Circular group reference is disallowed outside <redefine>. That is,
unless this element information item's parent is <redefine>, then
among the [children], if any, there must not be an <attributeGroup>
with ref [attribute] which resolves to the component corresponding to
this <attributeGroup>."

So, is it impossible to redefine a Model Group, or is there some other
syntax to accomplish it?

Thanks,
Bill