Re: finite universes

From: Ian Horrocks (
Date: 09/25/02

  • Next message: pat hayes: "Re: finite universes"
    Axioms that I write down do not assert anything about *the* universe,
    whatever that is, they just constrain the kinds of of models I want to
    reason over in some particular context. E.g., in a database context,
    querying could be viewed as saying something like "assuming that what
    I have here are all the tuples/elements in the universe, does it
    follow that ...". This does not mean that I am asserting that what I
    have here really are all the tuples/elements in *the* universe.
    Taking your argument to its logical conclusion would mean rejecting
    pretty much any assertion you could make as it is bound to be false
    w.r.t. something somewhere on the web.
    On September 24, pat hayes writes:
    > Ben and Ian, a point I should have made but didn't in todays telecon 
    > discussion. Ian introduced his example where one asserts that the 
    > universe has one thing in it. I said that it seemed crazy to me to 
    > assert that the universe was finite. Ben said in response that often 
    > one did want to work with a finite universe in databases, for 
    > example. Then we had a long discussion which I now think was beside 
    > the point. The key point, to me, is that when we are working in a 
    > web-logic context, any kind of restriction of the topic has to be 
    > made explicit, since there cannot be any kind of global guarantee 
    > that others will share those limited assumptions. This applies to 
    > things like closed-world assumptions, and to assumptions about 
    > working in a finite universe (which are really the same thing). I am 
    > not arguing that a web logic should ignore or disallow database 
    > ideas, or fail to provide for users who wish to utilize information 
    > from finite data stores, or information which depends on that 
    > finiteness; but all that can be done, and discussed, without anyone 
    > asserting the the *universe* is finite. All one needs to do, and what 
    > I think we should both say that they must do, and provide tools to 
    > enable them to do it, is to say that they are restricting themselves 
    > to some finite class of entities. But that restriction needs to be 
    > made explicit somehow - if only buried in an XML prefix in a file 
    > somewhere, not necessarily in an in-your-face kind of way - when that 
    > information is published in a web context. That is not, to emphasize 
    > the point, in any way an attack on the use of database technology or 
    > ideas, or in any way an attempt to marginalize or discourage existing 
    > applications or domains of use. But it does mean that I think that it 
    > is quite OK for a web *logic* to reject as inconsistent any assertion 
    > that the universe of discourse is finite, or only has one thing in 
    > it, or whatever: because that is not an assertion about your 
    > database, but about the entire logical universe of discourse for the 
    > whole semantic web. And saying that THAT is finite is indeed crazy, 
    > or at best a very strong philosophical claim that you had better be 
    > prepared to defend if you want to try to convince everyone else with 
    > a web browser of it. But in fact, you probably didn't want to say 
    > that in any case; you probably wanted to say that some subclass of 
    > the universe was finite, and to restrict yourself for the time being 
    > to that class; and of course I have no problem with that kind of 
    > assertion. I bet you would include the qualification, in fact, in any 
    > public data transmission, even if it were only implicit in some 
    > mutual convention that you and your friends were using.
    > Pat
    > -- 
    > ---------------------------------------------------------------------
    > IHMC					(850)434 8903   home
    > 40 South Alcaniz St.			(850)202 4416   office
    > Pensacola,  FL 32501			(850)202 4440   fax

    This archive was generated by hypermail 2.1.4 : 09/25/02 EDT