Surely the problem is not so much, or not just, some fuzziness in
nature, but also the need for different classification criteria
or facets. (01)
For example I can classify certain things as marine animals
regardless of where they sit in the Linnaeus classification, so
whales are both mammals and marine animals. (02)
The problem IMHO comes when data modelers who like to force
everything into a single classification hierarchy, try to
shoehorn things in based on differing criteria. The ISO
clssification for financial instruments suffers from this
unfortunate tendency. (03)
I expect that for many semantic web applications this temptation
arises also, based on a need for a model that is simple enough to
be able to carry out specific semantic web operations on, i.e.
where applications need a more decidable sub-set of terms than
nature (or the Indian Forestry Commission) readily allows. (04)
The solution to at least this part of the problem would be if
ontologies were able to have standardized metadata that
identified a "Classification Facet". Then it would be possible to
reach into the (business domain) ontology and pull out only those
terms which are classified according to a given facet (e.g. their
DNA, their habitat, who grows them etc.), as appropriate for a
given database application, or for a given semantic web application. (05)
What will be left behind will be some true fuzziness as you
suggest, and changes to the classifications (as when the Taxonomy
of Species moved from phenotypical to genotypical
classifications). But many of these should be definable in terms
of the facts that are used to define the different
classifications, and the granularity / ontological commitment
etc. of the things which those facts refer to (i.e. the ranges of
the object properties, in OWL-speak). (06)
On 06/07/2011 17:45, John F. Sowa wrote:
> This forum has been quiet for a while, and I'd like to stir the pot
> with a controversial issue.
> Two widely known rigid classifications established a paradigm,
> which some people mistakenly consider the norm: the periodic
> table in chemistry and the Linneaen taxonomy of living things.
> But the rigid boundaries of those categories are the result of
> underlying laws of nature that explain why intermediate cases are
> impossible (periodic table) and rare (taxonomy of species).
> For physics and chemistry, quantum mechanics implies discrete steps,
> which create discrete classifications of elementary particles.
> At the next level up, it also implies discrete combinations of
> such particles -- combinations of quarks to form baryons (protons
> and neutrons) and combinations of atoms to form molecules.
> For biology, discrete molecular operations support the stable
> molecules needed for life and the mechanisms for replicating the
> huge molecules needed for DNA. But those mechanisms are only
> weakly stable -- that leads to random mutations.
> For the next level up, natural selection creates fuzzy boundaries
> among interbreeding populations, but crisp boundaries between
> isolated populations. For example, look at the sharp distinction
> between foxes and wolves, but fuzzy boundaries among dogs. When
> humans allow dogs to "do their own thing", the breeds quickly
> revert to a generic ur-dog -- which is usually healthier and
> more robust than many breeds.
> Some biological classifications are not based on DNA. Examples
> are trees and berries. For example, the family Rosaceae includes
> rose bushes, apple trees, and raspberries. Biologically, all
> berries are fruit, but apples are more likely to be grouped with
> oranges as "typical" fruit than with raspberries.
> By height and woodiness, an apple tree is more likely to be
> classified with a remotely related spruce tree than with
> a rose bush. And many evergreens become bushes or trees
> at the whim of some human with a pair of shears.
> There is even a debate in India whether bamboo should be
> classified as grass or tree: "Recently there was a controversy
> when the union ministry of environment and forests asked states
> across India to recognise bamboo as a minor forest produce."
> See http://www.bbc.co.uk/nature/life/Bamboo
> In general, what makes any classification rigid is some *law*,
> which could be a law of nature or some human rule. Since it's
> a lot easier to change human laws, such classifications are
> likely to change with culture, technology, or fads.
> Summary: Fuzzy boundaries are the norm in most classifications.
> Whenever a boundary seems to be sharp, look for some axiom, law,
> principle, or convention that creates the distinction. Those
> laws are more fundamental than any grouping by "similarity".
> And a warning: Unless you can find an immutable law of nature
> that creates a classification, don't expect it to be a solid
> foundation for a "standard ontology".
> John Sowa
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