On 3/5/07, John F. Sowa <sowa@bestweb.net> wrote: > > Yet every SQL database > permits arbitrary first-order constraints. > > Q: How is possible to prove that the constraints are consistent? > > A: Trivially. > > The point is that no database designer *ever* begins with > an arbitrary set of constraints. They *always* begin with > some actual data -- a sample DB that shows what kind of data > they expect to work with. Simple idea that comes to my mind immediately: the DB is a *closed world*, i.e. if something is not there, this does not hold. It is different for the DL, which is an *open world*. That means if some fact is not known to be true, it can be either true or false (in a particular world). This means, that the search space is exponentially larger in case of description logic comparing to DBs. > John Best, Dmitry.Received on Tuesday, 6 March 2007 20:38:53 UTC
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