[sc34wg3] Question on TNC / Montreal minutes

Lars Marius Garshol sc34wg3@isotopicmaps.org
05 Sep 2002 08:49:36 +0200

* Jan Algermissen
| How interesting...this raises the question if the
| 'causeTNCbasedMerge'-flag is a property of a) the basename or b) the
| particular association between the topic and its base name.
There is no Reference Model draft yet, but it seems clear to me that
in the Reference Model this will be represented using two different
assertion types. The XTM syntax chosen to some extent obscures what is
conceptually going on: topics can have two kinds of base names,
identifiers (subject to the TNC) and labels (not subject to the TNC).

So the answer is neither a) nor b).

| If it is a) then the above topic map would not be valid I think,
| because a basename would either be triggering a merge or not. This
| also seems to demand that the value of the merge attribute has to be
| the same for all basenames that are equal.

Requiring that would basically break the whole solution, since the
point of being able to say merge="off" is to avoid unwanted merges.

| But then, isn't it the topic map processor that eventually decides
| how it interpretes 'equal' ? 

No. The SAM specifies this very clearly. Strings are equal if they
consist of identical sequences of abstract Unicode characters. In
other words, matching is case-sensitive and Unicode normalization is

To leave this up to processors would mean that subject identity would
not be treated reliably, which would more or less guarantee breakage
of topic maps upon interchange.

*Applications*, on the other hand, are free to use whatever rules for
merging they please, but that's different from what *processors* are
required to do.

| This would then lead to a situation where a map might be valid in
| the context of the author (suppose the author thinks of
| 'char-by-char' equality) but might be invalid for some topic map
| engines (that propably apply a case insensitive interpretation of
| 'equal')....???

| If it is b) then the merge attribute should be on the <baseName>
| element and would mean: "whatever other pieces of the map say, don't
| merge this topic with other topics that happen to have the same name
| (in the same scope).

The attribute is on <baseNameString>, because it does not apply to the
variants, but it does say what you think here.

Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
ISO SC34/WG3, OASIS GeoLang TC        <URL: http://www.garshol.priv.no >