On 03/06/13 16:52, Phillip Lord wrote:
Value unknown is easy. Just don't say anything. Value not applicable and doesn't exist, given your examples, seem the same to me.
I don't agree. Under the Open World assumption anything that can later be learned should not affect consistency. A positive null ("there is no such") should lead to a contradiction is someone later asserts such a value/relationship (which doesn't happen with a simple unpopulated relationship from the subject).
In RDF (which has been my answer before - feel free to contradict me, I'm not an authority, it's just that I've made the proposal before) this seems possible only with Collections. What I mean by this is that with a list-ranged relationship I can specify a value of 'there is no such' (rdf:nil) and someone trying to populate the list later would have to revert that fact to provide such a value. Without a list expected, this does not seem possible (again, to me).
Barry
