Tim Bray's challenge for a Really Useful application to donate the domain rdf.net to has led to one submission: McCullough Knowledge Explorer and the MKR language
Unfortunately the description says :
McCullough Knowledge Explorer (MKE) is an interactive tool for organizing knowledge. It helps the user to record, change and search knowledge, and provides extensive error checking to ensure the internal consistency of the knowledge.
That's doom for the product in one sentence. In closed domains maybe consistency works, but the distributed nature of the web simple has no place for notions like consistency. If it is consistent most of the time, fine - but it certainly not a design parameter of knowledge that it be consistent across meaningful volumes of information. If it were we'd be running out of words in no time.
Knowledge is always situational, and the best description of knowledge is "whatever pre-learned rules that are effective in a situation that you find yourself in". Adding more language than that puts you in the space of formal models very fast. You can start by namespacing the situational contexts and trying to make each of them consistent, but you will run into problems almost immediately if the namespacing is anything but an enumeration of situations and interpretations that have occured.
I think the theory of semiotics and signs, with the notion of infinite semiosis (i.e. reinterpretation) and no barriers at all to what constitutes signing (i.e. ideas or meanings) has it right.
As evidence of how tangled meaning is - surf the New Testament HyperConcordance. That's the full text of the New Testament, with every word indexed, and with every occurence of a word hyperlinked to the index. In short - A screenful of blue links.