[sc34wg3] Identifying and comparing subjects (and a possible extension to \tau )

[Robert Barta]

On Sun, Aug 01, 2004 at 01:42:21PM +0100, Ann Wrightson wrote:
> This has been (since 2000 ;-) my main argument against merging always being
> an a+b=c kind of operation that loses the fine structure of a & b. I believe
> that there should also be a different operation that both preserves the
> original maps and defines a view-as-if-merged-according-to-this-mapping. 

Ann,

I completely agree, and - as Lars mentioned - it is not prohibited by
the current standards to keep the original maps.

Also for \tau this is no problem...

> I'm realizing as I write that this suggests a different formal account of
> merging - call it merge2 - eg (in \tau) where the two maps being merged have
> different sets of names (curly N1 and N2) in the universe (curly I) and
> instead of merge2 being a set union, it is a function where the desired
> property of "preserving information" from the source maps to the target maps
> becomes a morphism property of the function.

...because:

  - The 'elementary composition' only merges assertions if EVERYTHING
    in them is the same. This means that the identifiers have to be
    EXACTLY the same to trigger merging according to sets.

  - If, for some reason, you do not want this kind of merging to happen,
    simply rename all identifiers to arrive, as you say above, at two
    distinct name sets N_1 and N_2.

    If we build A + B now, we simply drop all assertions into a big
    pot. Nothing will be merged then.

  - If a more sophisticated merging is necessary, then our query
    language kicks in! Since we allow TMQL to produce topic maps,
    we can create a query which honors the merging condition and
    which creates a newly consolidated map.

    See

       http://topicmaps.it.bond.edu.au/docs/23/toc

    for a taste of this.

    For some fixed merging rules, this can be hard-coded into
    our programs, like for the infamous "name-based" or "we-share-
    subject-INDICATORS", so to have the proper performance.

\rho