[topicmapmail] Two Models of Facets

[Murray Altheim]

Thomas B. Passin wrote:
> Murray Altheim wrote:
> [Tom PAssin wrote]
> 
>>>...As a matter of practical performance when retrieving by facet 
>>>collections, this scheme would probably be miserable for a large map 
>>>using a general purpose engine, so I would probably look to create 
>>>customized data structures and methods for handling the facets.  I 
>>>would like the topic types for the roles and the facet association to 
>>>be PSIs, so that my engine would be able to recognize when to use the 
>>>custom features.  This would not prevent me from serializing out to 
>>>XTM, since it would just be application-specific customization.
>>
>>I don't see this as any more a performance hog than any other scheme of
>>similar power. If I want "all Topics playing the role of 'blue' in a
>>'hasEyeColor' association", where that's implemented in the model won't
>>have a huge impact on the amount of information modelled. And my guess
>>is that simply using an FC model would have some benefits for understanding
>>the structure of the ontology, just as people now use slots rather than
>>putting everything at the same level of the model.
> 
> My thought was that there would be a *lot* of retrieval by role, since 
> you need many facets to establish the topic of interest.  Thus the role 
> machinery (and any inferences using it) would be worked especially hard 
> and therefore would probably need tuning and more careful design.

Remember that "roles played in associations" is one of the fundamental
topic characteristics, so if there are Topic Map engines that aren't
tuned to handle that, maybe this is a good thing. It's all part of the
big graph in the sky.

>>Heck, I can imagine that a facet might serve as a facet type for itself.
>
> Hmm, I don't quite get that one yet ...

Any time a topic may also be a characteristic of the same topic, i.e.,
any time there's recursion in a definition.

>>As to the method of attachment, in XTM it'd just be a specialized
>>association type, in the same way we now understand that occurrences
>>are just a specialized association type. 
> 
> Right, but would the facet hierarchies by in associations, roles, or the 
> role-playing topics?  For a single faceted classification of a topic, I 
> see a single facet associatiom with a role for each facet.  The 
> role-players would supply the location in the hierarchy.  But obviously 
> there are other ways to do it.

Yes, I think there are several ways to do it, hence this thread. If we
came up with a common model for doing what I'm thinking of as these
two types of facets, it's certainly possible to optimize Topic Map engines
to handle these things. Since facets are in ISO 13250 (I think the Model A
ones), it'd be in the interests of developers of those engines to do that
optimization. Ideally, I'd like to see both Model A and T facet machinery
"standardized" to some reasonable degree.

>>But we'd first have to nail down
>>*one* definition of facet, which is kinda what I'm trying to do here.
> 
> Well, whatever it turns out to be, let's make sure NOT to insist on 
> exhaustive, fully orthogonal facets as the classic definitions like to 
> insist on.  I consider exhaustivity (is that even a word???) and 
> orthogonality to be hard-to-impossible to achieve in most practical, 
> everyday situations.  Would you agree with this view?

Yes, absolutely. It's always possible to create a more complicated
model of anything using PSIs, to overlay on a Topic Map/TM engine. I'm
predominantly interested in codifying the two facet models I've described,
one as a "competitor" to RDF in assigning metadata to resources, the
other as a way to assign to a Topic either other Topics or property values,
as facets. And then the easiest, most reasonable way to do that in XTM.

Murray

...........................................................................
Murray Altheim                         http://kmi.open.ac.uk/people/murray/
Knowledge Media Institute
The Open University, Milton Keynes, Bucks, MK7 6AA, UK                    .

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      http://www.nationalreview.com/comment/comment-singer062002.asp
      http://www.iraqinews.com/people_chalabi.shtml
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   A: One speaks fluent Arabic, the other Spanish.

     "Noriega took refuge in the Vatican embassy, where US troops played
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      http://www.nationmaster.com/encyclopedia/Manuel-Noriega
      http://www.gwu.edu/~nsarchiv/NSAEBB/NSAEBB2/nsaebb2.htm#3a
      http://www.addictedtowar.com/panama.htm