There are a number of themes in Clay's post. The primary theme appears to be one of completeness: Clay's thesis is that the vocabulary is incomplete because it doesn't provide properties to model composite relationships: what if you are employed by a colleague you collaborate with?. Clay seems to be implying that he expects the terms to be exclusive. Of course they're not. It's perfectly meaningful to assert that
Jane employedBy John and
Jane collaboratesWith John. RDF supports this kind of assertion and you can also express it with the HTML method outlined in the vocabulary.
There is a second theme which is an accusation of hubris on the part of Eric and myself. By publishing a polished and updated version of a 15 month old vocabulary we have become as gods, able to control all manner of human expression. Clay suggests that the terms that we left out are somehow verboten. Of course it's true that you can't use our relationship vocabulary to say
Jane gotArrestedWith John but the semantic web, as with all other forms of human expression is not limited to a prescribed list of verbs and nouns. The relationship vocabulary is no manual of newspeak, more a tiny copy of Johnson's dictionary. There are many more dictionaries waiting to be written and some of them will allow you to say any or all of the things that Clay suggests he needs.
Maybe there's a third theme here also: imperfection. The relationship schema is imperfect. Here we agree. The surprise is that Clay expects it to be perfect. On the one hand he says that relationships are messy to model and on the other he derides the vocabulary because it's messy. Which is it to be?
Obviously I'm pleased that Clay has taken the vocabulary seriously enough to critique in detail. Somehow the thought that everyone would ignore it caused me more concern than the fear that everyone would hate it.
Despite all the obvious thought Clay put into his piece, he still managed to overlook the raison d'etre for the relationship vocabulary. Indeed it's the raison d'etre for all vocabularies. Without these vocabularies, incomplete and imperfect as they are, we would be mute in the machine readable web, unable to express ourselves in any meaningful way. You only have to look at the etymology to realise that vocabularies give you a voice.