TMDM and merging associations

Hello everyone,

I was checking some details of the Topic Map Data Model for our Wandora
project and I found something in the specification that I thought
somewhat strange. I thought the correct way to to merge associations
would be to simply make the roles property the union of the roles
properties of the two merging associations and then merge equal roles.
Instead the specification tells you to "Set C's [roles] property to the
value of A's [roles] property. B's value is equal to that of A and need
not be taken into account." This doesn't seem to take into account the
possibility that the roles of B may be reified and the reifications need
not be anything similar to those of the roles of A. After the merge, the
merged association C would have no link to the topics that reified roles
of B. Depending on how you implement the data model you might even end
up with a situation where some topics in the topic map reifiy roles that
are no longer part of the topic map at all.

Since merging of association roles is well defined and takes care of any
reification issues, even when both roles have a reifier, it would seem
logical to merge associations by merging roles of both associations.

Regards,
Olli Lyytinen
Wandora Team