Re: defaults

I am not sure what Dab refers to when he says he has no need for
defaults in indexing/searching collections. Let's take a simple example.

A person wants to search for images of a "red ape". Most photos of
orang-utans
will match this query. However, one cannot expect the indexer of every
orang-utan photo to state explicitly the color of the ape (this also
leads to unwanted inter-indexer variability). You really
want them to link the photo to the class "orang-utan", and possibly
only specify the color if it is not red (old animals can get
brown/grey, there are albino orang-utans, etc.). If we do not allow
the specification of the default color value for orang-utans in
general, we will not find these matching photos. I thought this was what
the semantic web was all about....

For more information about orang-utans, see for example the website of
the ARkive project at http://www.arkive.org.uk (our COLLECT use case
1). The orang-utan is an endangered species. Incidentally, it also
shows a nice example of "classes as instances". An "orang-utan" is
an instance of a "species" class. 
I enclose part of the orang-utan species instance description (taken
from the same website): 
 
Orang-utan (Pongo pygmaeus)
  kingdom: Animalia
  phylum:  Chordate
  class:   Mammalia
  order:   Primates
  family:  Hominidae
  genus:   Pongo

Note that specifying orang-utan as subclass of species (and defining
the vales above as slot-value restrictions) is incorrect. An
individual orang-utan is not an instance of "species". 

Guus

-- 
A. Th. Schreiber, SWI, University of Amsterdam, Roetersstraat 15
NL-1018 WB Amsterdam, The Netherlands, Tel: +31 20 525 6793 
Fax: +31 20 525 6896; E-mail: schreiber@swi.psy.uva.nl
WWW: http://www.swi.psy.uva.nl/usr/Schreiber/home.html