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.htmlReceived on Thursday, 24 January 2002 10:39:25 UTC
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