Doc references are based on formal/03-05-02.
In a Schema that is produced by the XML Schema Production
rules, enforcement of multiplicities is incompatible with
the use of proxies.
According to 1.10.1, page 1-21, "Elements act as a union,
where they are either a definition or a proxy. Proxies use
the LinkAttribs attribute group to define the link, and
contain no nested elements."
However, if the org.omg.xmi.enforceMinimumMultiplicity is
true, then the generated schema does not allow the complex-
Type's content to be empty, and so proxies cannot exist in
an XML document.
As a simple fix, the 4b:ClassContents could be wrapped into
an additional choice element, as in
This would allow the element to be empty. However, in this
form, an XML document that contained both link attributes
and contents would still validate.
A stronger solution would be to make a choice between a
link element and contents, by removing the LinkAttribs from
the ObjectAttribs attribute group and by, in rule set 4,
defining something along the lines of
<xsd:element name="href" type="xsd:string">
<xsd:element name="idref" type="IDREF">
This way, an element in a validating document could only be
either a proxy or not.
As a side note to this issue, there are obviously unpleasant
side effects when org.omg.xmi.enforceMinimumMultiplicity is
true and org.omg.xmi.element is false. org.omg.xmi.enforce-
MinimumMultiplicity=true should have the same effect as
if org.omg.xmi.element=true and org.omg.xmi.attribute=false.