- From: Michael Schneider <m_schnei@gmx.de>
- Date: Wed, 24 Jan 2007 15:02:00 +0100
- To: richard@cyganiak.de
- CC: semantic-web@w3.org
Richard Cyganiak wrote on Mon, 22 Jan 2007: > You say that there exist indeed two different kinds of things in a > domain: entity-like things and relationship-like things. You cite the > example of natural numbers, which clearly are entity-like. > > You are right in the case of mathematics, a domain that comes nicely > pre-packaged in elements and sets. But many domains are not like > this. Take, for example, the concept of a "married couple". Is this a > relationship-like thing that should be modelled as an RDF triple > connecting two resources? Or perhaps as a distinct resource that has > connections to the two person resources? Or perhaps as a two-element > class? The answer is that all these options can be reasonable, it > depends on the concrete use case. Thus my claim that entity-likeness > or relationship-likeness is an artifact of modelling and not inherent > to the world. "Twin primes" would have been a really insidious counter example! ;-) Well, ok, it's probably not that easy, as I suggested. And such a debate isn't my focus in this thread, so let's assume here that it's allowed to have all three proposed views on such a "married couple" resource expressed together within the same RDF graph (without getting a meaningless interpretation). I will denote this resource (it is a resource within the domain, at least, whatever more specific nature(s) it actually has) by URI ':aliceAndBob' in my graph. 1) Seeing it as a thing-like resource, we can assert, for example, that it is an instance of some class: :aliceAndBob rdf:type :MarriageCouple . In RDF(S), this triple has a defined meaning, so everyone (and every reasoner) who knows RDF(S) semantics, also knows what this triple is meant to express: That the thing-like resource denoted by URI ':aliceAndBob' is an instance of the class-like resource denoted by URI ':MarriageCouple'. 2) By regarding it as a class-like resource, we can write down the following triples: :alice rdf:type :aliceAndBob . :bob rdf:type :aliceAndBob . Again, it's clear from RDF(S) semantics, how these triples have to be understood. 3) Last, seen as a relationship-like resource, I would, for instance, like to state, who is the left-hand-side of this relationship, and who is its right-hand-side, and what relation actually holds between them. But, regrettably, in this case, RDF doesn't directly provide me some means to model this, so I have to invent my own method: :aliceAndBob :hasLeftHandSide :alice ; :hasRightHandSide :bob ; :relation :isMarriedWith . Works, of course... But a little more language support would make me even more happier! :) Cheers, Michael
Received on Wednesday, 24 January 2007 13:52:54 UTC