Problems restricting UBL's AddressType complexType

Hi, 

I've spent several hours trying to figure out why I can't restrict UBL's
AddressType
(http://docs.oasis-open.org/ubl/cd-UBL-1.0/xsd/common/UBL-CommonAggregateCom
ponents-1.0.xsd) to remove certain elements. My (currently invalid) schema
attempting to do this is here:
http://groups.sims.berkeley.edu/EventCalendar/UCBAddress.xsd. I am only
trying use restriction to remove elements that are minOccurs="0", and many I
was successfully able to remove. However, when trying to remove elements
that are part of AddressType which look like this:

<xs:element name="ID" type="udt:IdentifierType" minOccurs="0" maxOccurs="1">

I'm told by Oxygen that: 

Description: E derivation-ok-restriction.5.4.2: Error for type
'UCBAddressType'.  The particle of the type is not a valid restriction of
the particle of the base.

URL: http://www.w3.org/TR/xmlschema-1/#derivation-ok-restriction

AND

Description: E rcase-Recurse.2: There is not a complete functional mapping
between the particles.

URL: http://www.w3.org/TR/xmlschema-1/#rcase-Recurse 


I read the spec and it *seems* that I've met all the requirements, but the
spec is a bit hard to read. I simply copied AddressType from the UBL schema
to begin building my restriction so I'm not sure what I could be missing.
Any help would be much appreciated!
 
Allison Bloodworth
Principal Administrative Analyst
e-Berkeley Program Office
University of California, Berkeley
(415) 377-8243