From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 02/07/01
From: Jim Hendler <jhendler@darpa.mil> Subject: Re: added diagrams to "Using XML Schema Data Types..." Date: Wed, 7 Feb 2001 13:57:26 -0500 > At 12:40 PM -0600 2/7/01, Dan Connolly wrote: > > > > > >To have the parsing of one document depend on the > >contents of another conflicts with that goal/principle. > > > >Another way to state this principle is that > >the knowledge contained in two documents, X and Y, > >is always the conjunction of the knowledge in X with > >the knowledge in Y. To allow X to change what Y says > >in some non-monotonic way doesn't seem scalable/workable > >to me. > > > > I absolutely agree with the first of these and completely disagree > with the second, so maybe they're not exactly equivalent... since I > tend to like examples, here's one > > Web page 1 says: X is true > Web page 2 says: X is False > > The parsing of web page 1 or two is not changed by reading the other, > but I don't know a good monotonic way to combine these two without > problem (solution is for me to tag them, or reject them, or something > - but I need to be allowed to recognize conflict) > > web page 1 says: 1 is an integer > web page 2 says: 1 is a real > web page 3 says: 1 is not an integer > > are these cases inherentely different? I'm not sure, > > Prof. James Hendler hendler@cs.umd.edu > Computer Science Dept 703-696-2238 (phone) > Univ of Maryland 703-696-2201 (Fax) > College Park, MD 20853 http://www.cs.umd.edu/~hendler The *monotonic* way of combining these two sources is to be(come) inconsistent. This is perfectely fine logically, but probably not exactly what is wanted in a pragmatic sense. A better solution is to back out of the committment to one or the other, using some extra-logical information. As information has been removed in this process, there is no requirement of monotonicity. peter
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