From: Wagner, G.R. (G.R.Wagner@tm.tue.nl)
> Can we come > up with an n-ary representation that's significant simpler or > otherwise better than the unary/binary SWRL representation? What do you mean with "significant simpler or otherwise better"? The issue here is simply that "objectifying" a relation may be unnatural and create some undesirable (and unnecessary) overhead in the language. This is not so obvious in your examples, since it's natural to talk about diagnoses and purchases. In foundational ontology, one makes a distinction between formal and material relations (both of which would be represented with the help of predicates). In the foundational ontology GOL [1,2], there is the basic assumption that material relations (such as isMarriedTo/2, purchases/2, purchases/3, purchases/4) are based on a "relator universal" (i.e. the intensional classes Marriage and Purchase), while formal relations do not have such a basis and correspond to sets (extensional classes). If this is true, it's indeed no problem to reify material n-ary relations (such as "purchases/3" and "purchases/4") because there is a natural class (Purchase) as the domain of n binary properties replacing the n-ary relation, while it will be difficult/unnatural to reify formal relations suh as "between/3". -Gerd  http://www.onto-med.de/en/concepts/gol/index.html  Attached paper: G. Guizzardi1, G. Wagner, and H. Herre: On the Foundations of UML as an Ontology Representation Language. In E. Motta et al. (Eds.): EKAW 2004, LNAI 3257, pp. 47-62, 2004.
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