finite universes

From: pat hayes (
Date: 09/24/02

  • Next message: Ian Horrocks: "Re: finite universes"
    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.
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