XMI12 — Anomalies with References and ordered Associations.

In trying to implement a consumers for ordered Associations, I've
come across the following anomalies caused by References.

Consider the following metamodel:

package P {
class C1

;

class C2

;

association A1

association A2

The first anomaly is with the "r2" Reference. Since this "refers to"
the unordered end of an Association, the "value" of the Reference does
not contain any ordering information. But, since the Association has a
Reference, the links for the Association won't be output in an
<association-name> element. In other words, the ordering information
for the Association links will be lost. This is a serious problem. [For
the record, there is nothing "wrong" with the meta-model either IMO]

The second anomaly (or maybe it's just a "feature" ...) is with the
References "r1" and "r3". The problem is that while the xmi entities
generated for the "r1" Reference can be converted into links, this is
not true for the reverse "r3" References. Clearly, if I try to use
"add_links" on a C2 instance to set the "r3" Reference values, it is
next to impossible to get the ordering of the A1 links correct. This
makes the "r3" References next to useless ... as well as their being
redundant.

My preferred resolution to this issue would be to simply remove all
handling of References from XMI, and represent all links in the
<association-name> element.