[foaf-dev] Implying that two mentioned individuals are distinct... updating best practice from owl:differentFrom to owl:IrreflexiveObjectProperty?

From discussion here at benelux semweb meetup in Amsterdam -

In FOAF, if we say

alice a foaf:Person .
alice foaf:knows bob .
bob a foaf:Person .

..this implies the existence of at least one Person. It's truth
doesn't guarantee formally that there are at least two people, even
though the commonsense semantics of foaf:knows do require that it
relates different individuals.

Over in the relationship vocabulary, various properties are defined as
sub-properties of owl:differentFrom,
http://vocab.org/relationship/.html

This has the required meaning but throws the vocabulary into
(horrors!) the Full flavour of OWL, which makes it harder to use in
certain settings.

I asked Rinke about this today, as I'd like to add some OWL to FOAF's
definition that helps make implicit things that we are all assuming
anyway, ie. that Alice and Bob are different individuals.

He suggests http://www.w3.org/TR/2009/REC-owl2-syntax-20091027/#Irreflexive_Object_Properties
will do the job, and that this doesn't put the idiom into OWL Full.

So we would on this usage assert that rel:livesWith, foaf:knows and
similar relations are owl:IrreflexiveObjectProperty ie. that they
can't truthfully be used to assert of some resource r that it stands
in that relationship to itself.

The benefit is that we could then finally say that FOAF such as
<Person><name>Alice</name><knows><Person><name>Bob</name></Person></knows></Person>
can only be true if there are at least two distinct people. I think
this kind of commonsense logic is embedded in lots of application code
already, so it would be nice if we can update the formalities to match
deployed reality. Counting things based on RDF data is hard, since we
can't make the unique names assumption
(http://en.wikipedia.org/wiki/Unique_name_assumption), so any hints as
to number of mentioned entities can be useful when trying to relate
RDF data back to reality.

Unless I hear arguments to the contrary, I suggest adding this to the
FOAF schema. Perhaps it would be a good fit to add to rel: RDFS also,
whether augmenting or replacing the current content.

Ian - do you have the impression that anyone is using the
owl:differentFrom claims, or they serve essentially as (language
neutral) documentation of your intended meaning?

cheers,

Dan