Kees, take a look at this 'wordnet' resource...
On Wed, 9 Jun 2004, Mike Linksvayer wrote:
> Karl Ove Hufthammer wrote:
> > The point is: Images aren't placed in hierarchical categories,
> > they have keywords assigned to them. The hierarchy is a separate
> > thing.
> Good idea.
> Wordnet <http://xmlns.com/2001/08/wordnet/> may be useful here.
> Example: http://xmlns.com/wordnet/1.6/Flag
> If a keyword is known by Wordnet, a hierarchy is provided.