[sc34wg3] XTM 1.0-style reification and TMDM
Lars Marius Garshol
larsga at ontopia.net
Tue Oct 31 10:55:04 EST 2006
Lars Heuer brought up the issue of what happens when in a topic map
some construct and some topic have the same URI as item identifier
and subject identifier, respectively.
In XTM 1.0, this means that the topic reifies that construct. The
TMDM does not mention this issue at all, and neither does XTM 2.0,
since this is not an issue in XTM 2.0. However, we need to have an
answer on the data model level, where it applies irrespective of what
syntax(es) the various parts of the data originate from.
Having thought this over, my opinion is that in TMDM this doesn't
mean anything, just as it doesn't mean anything in XTM 2.0.
However, the question is what we do with XTM 1.0. We could say that:
(a) Reification is evaluated when we see a <subjectIndicatorRef/> that
points to the item identifier of some non-topic item. If this
case we have reification. The trouble is that this will give
results depending on the order of processing, so this doesn't
(b) XTM 1.0 is not our problem. All XTM drafts up until the one
the Atlanta meeting covered the new XTM as well as 1.0, but
we abandoned that policy, and now XTM 1.0 is only defined in the
old TopicMaps.org spec. (And what that means is anybody's guess.)
(c) Reification is evaluated at the end of the XTM 1.0 import. That
if there are any matching SI/II pairs, this is considered to be
reification. This is probably expensive to implement, however, and
a bigger issue is that SI/II pairs that didn't originate in the
XTM 1.0 file will also turn into reification.
(d) We could extend (a) and say that reification is *also* evaluated
whenever -id- attributes occur on non-topic elements. This would
rid us of the ordering problem, and should work for all imaginable
I think I have convinced myself that we can stick to the line that
this doesn't mean anything in TMDM, and that the old XTM 1.0
reification can be confined to XTM 1.0. The only problem with this is
that we have no official document to write this up in, but then we
have no official document specifying the rest of the XTM 1.0
interpretation, so I guess this isn't really an issue.
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