For sure there are going to be some applications that need some degree of certainty. Say an RDF-based application that manages your home’s security. You ask it, “Has anyone broken in?” and it responds, “Now just what do you mean by broken in?” Or, “There’s a 90% chance no one has broken in.”

On the flip side, a model that allows you to say things with certainty doesn’t force you to do so. So if people have chosen non-collided URIs for roughly the same thing, while RDF may say that they are not-certainly the same thing, you can still apply the same heuristics (whatever they are) to get a probabilistic answer. Often entities have a rdfs:label anyway that you could use for that.

Your example with FOAF actually relies on the fact that the foaf:mailbox property is reliably interpreted by applications as what it is. Applications don’t have to first ask “is the foaf:mailbox property here the same as the foaf:mailbox property there?”

So what you’re really saying is that you want a system where it’s impossible to say anything with certainty. You could have that if you want, but then that system is just solving a different set of problems that RDF solves. Plus, compare that to the system we have now where it’s possible to say things with certainty if people want to do so, but there’s nothing preventing heuristic comparisons either (as you pointed out with FOAF).

Plus I think the idea that “disambiguation of natural language terms can be tractably (and often trivially) achieved” is really unlikely (being a linguistics grad student). On a large scale, I would have to see it to believe it.

Unlike del.icio.us which uses simple words to connect pieces of information, the Semantic Web proposes to use URIs so that you really know when two people mean the same thing. Phil Dawes echoes my feelings on this design issue:I still…

In the foaf case you’re relying on the client to have understood that ‘http://xmlns.com/foaf/0.1/mbox’ is an IFP property requiring a unique personal mailbox and not one e.g. shared with a spouse. So we’re talking about sliding scales of confidence here, not absolutes.

Using a description framework ala RDF allows you to disambigate terms through their relationship to other terms. This is a proven technique in natural language and translates well to software: Applications have knowledge of the problem domain they’re operating in and the combination of terms they’re expecting to operate with. That combination of terms provides a trivial way to disambiguate data from disperate sources. Besides, you can always add disambiguation metadata to your descriptions:

<> type FoafPerson
<> usesTermsFrom http://www.foaf-project.org/
<> name "Phil Dawes"
<> surname "Dawes"
<> homepage http://www.phildawes.net/
<> mbox phil@example.com

Also you tend to find that where there are global areas of ambiguity humans tend to invent names and schemes which have a low chance of collision. Email addresses, vehicle number plates, URLs and names like ‘FOAF’ are examples of these. These are already grounded in real life, widely shared, and are ripe for use in data exchange.

I see your point about even URIs being on a fuzzy confidence scale. But there’s a difference. The uncertainty in URIs is about whether the author has typed in what he intended to convey. That probability is fairly high in general, and it’s an easy and useful assumption to ignore the possibility that an author simply made a mistake. In practice, we can get away with that pretty well.

But if we have to rely on heuristics to tie together every name, there are a lot more parameters to consider besides the one parameter for probability of a mistake. How exactly do you compute the probability that the “Phil Dawes” on this page is the same one mentioned elsewhere? At the very least you need to know how many Phil Dawes there are in the world. These aren’t parameters that are easily abstracted away.

So I guess what I’m saying is, of course everything is fuzzy in the real world, but there are some types of fuzziness that we often want to ignore for the sake of building an application that is going to give us a yes/no answer, or an answer whose certainty is only contingent on whether we think the authors of the data were competent enough to have written it out correctly. We can deal with that type of contingency, but that’s not available to us if the whole system is ambiguous.

I believe this is the major problem remaining to be solved for the semantic web. Sure, you can mint any URI, and by definition of the formal system - whatever it is that is denoted by that URI by me shall be the very same concept that is denoted by you. The problem is that it is still necessary for me to communicate to you and our machines, unambiguously if possible, what exactly I intend to denote by that URI. How am I supposed to do that? Our if I am the audience, how am I supposed to know how to interpret that URI so that I understand the same concept you had when you published it?

And its not just a matter of mistakes, carelessness, or incompetence. Nor is it really a failing of URIs or RDF. The real problem is that the world itself does not come neatly divided into conceptual categories. It presents as a very nearly continuous whole, and we each parse it up as best we can, depending on our context, or history, and many other factors. I have posted about this before, It Takes an Agent to be Semantic. Before we can really use that URI to communicate then, we must somehow bring our interpretations into alignment, we must establish a common ground of interpretation. I have proposed an proposed an approach to this in Creating a Common Ground for URI Meaning. Lately I’ve come to think of common ground as synonymous with utterance (or statement) context and now think that the meaning of a URI is its location in the context of the semantic web

What I’m looking for now is how to represent this context of common ground in OWL. I’m trying to build an ontology of context.

Thanks in advance.