On 06/08/2008 09:54, "Yves Raimond" <[EMAIL PROTECTED]> wrote:
> > > Hello! > ... > > I am not sure if I interpret it correctly - do you mean that you could > link to two URIs which are in fact sameAs in the target dataset? > Indeed, in that case, the measure would be slightly higher than what > it should be. However, I would think that it is rarely (if not never) > the case. > ... I think not. In our set of KBs this (or similar) is already the case, and vice versa. And it is about to get worse on a world-wide scale. Consider: I have URIa and I have done a lot of work to discover that I think that URIb and URIc (from another source) should be considered the same. (In fact, one of the things that gives me confidence is that I found this other KB I had some trust of that made the same assertion.) Clearly I could just assert URIa owl:sameAs URIb. But then my knowledge that URIa owl:sameAs URIc becomes fragile; it depends on my users finding the other KB, on that KB continuing to exist, and that the other KB does not change its mind. The only safe thing to do (unless I want to risk losing the knowledge, and the work I put in to glean it) is assert URIa owl:sameAs URIc myself. Now the situation you describe has happened. The inverse is a little more robust. The KB with URIb and URIc had worked out that URIa is the same. They can just assert URIb owl:sameAs URIa and trust to the continued knowledge of the sameness of URIb and URIc. But the really safe thing to do is also assert URIc owl:sameAs URIa, so the knowledge will be preserved if knowledge of URIb changes or indeed the URI is removed or somehow deprecated. Of course this argument can be extended as more URIs are discovered. This is the nature of using a binary relation in this way, and results in an O(n squared) graph. You can take architectural steps to reduce it, introducing canons and things like that, but the fundamental big O problem is still there. Best Hugh -- Hugh Glaser, Reader Dependable Systems & Software Engineering School of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ Work: +44 (0)23 8059 3670, Fax: +44 (0)23 8059 3045 Mobile: +44 (0)78 9422 3822, Home: +44 (0)23 8061 5652 http://www.ecs.soton.ac.uk/~hg/ "If we have a correct theory but merely prate about it, pigeonhole it, and do not put it into practice, then the theory, however good, is of no significance."