Re: added diagrams to "Using XML Schema Data Types..."

From: pat hayes (
Date: 02/07/01

At 7 Feb 2001 13:57:26 Jim Hendler wrote:
>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)

It's easy to combine them monotonically: you get a (monotonic) 
contradiction. (What you do next isn't a monotonic reasoner's problem 
area, it just finds them and books them.)

>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


WP1 says: a is an integer
WP2 says: b is a real
WP3 says something about: a+b

Should we expect a parser looking at WP3 to be able to figure out 
what '+' means ?
Peter's position (?) is that it is reasonable for a parser to require 
that it know some things about what its trying to parse.
Dan's position (?) is that because of examples like the above, such 
requirements would violate web-logic principles.

My position is that Dan's conclusion only follows if he also insists 
that everything be locally parsable, but a better (more realistic) 
requirement is only that it be locally checkable whether or not it is 
parsable, ie the monotonic conclusion one really needs is whether or 
not there is enough information available to proceed monotonically. 
Then one of Peter's parsers wouldnt die or do something nonmonotonic 
when faced with WP3, but it might have to wait, or complain, or ask 
Google to find out something about a and b, or something like that.
And life is going to be like that whether we like it or not, so we 
might as well face up to it now.


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