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Re: log:notIncludes (conclusion?)

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Sat, 27 Aug 2005 16:22:01 -0400
To: jos.deroo@agfa.com
Cc: sandro@w3.org, public-rule-workshop-discuss@w3.org
Message-Id: <20050827202201.79111CB5D3@kiferserv.kiferhome.com>

> I was also thinking like that Sandro, but Michael argued and argued
> and I was not able anymore to counterargue.. Looking back at
> http://lists.w3.org/Archives/Public/public-rule-workshop-discuss/2005Aug/0090.html
> Michael, your set A is
> 1.   { <uri-of-document> log:semantics ?F.
>       ?F log:notIncludes { sky color blue } }
>                    => { thisTest a Pass }.
> 2.   fred hairColor red.
> but what exactly is the logical connective between 1 and 2?
> I'm pretty sure it is *not* logical AND: the triple in 2
> (which lives at <uri-of-document>) is *not* asserted in my
> engine whereas the triples/rules in graph 1. are asserted.
> I mean, if you ask cwm or euler to prove  fred hairColor red
> you would simply get no proof, as that triple is not asserted.
> If it is not logical AND then how can one talk about adding?

Yes, because you have a luxury of a "logic" language without the
normal logical attributes: a semantics and a proof procedure that is at
least sound with respect to the semantics.

I was trying to make a logical sense out of it. The fact that your engine
doesn't say that fred's hair is red is just a property of your engine,
which does what it does. Since N3 has no semantics, I can't say whether the
answer is correct or not.

If I were to give a reasonable logical semantics to N3, I would have said
that the formulas sitting at <uri-of-document> are asserted and true.  The
log:semantics predicate is a meta-logical means of reflecting (reifying)
those formulas; it makes lists out of the true formulas sitting at

There is a long way to go from here to a reasonable semantics, but it is a

When I was "arguing and arguing" I had this severely under-developed
semantics in mind. At least, it gave me a way to think of what was going on
in logical terms. In the absence of ANY semantics of this kind, our entire
discussion about monotonicity is meaningless.


> Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/
> Sandro Hawke <sandro@w3.org>
> Sent by: public-rule-workshop-discuss-request@w3.org
> 27/08/2005 20:51
>         To:     Michael Kifer <kifer@cs.sunysb.edu>
>         cc:     public-rule-workshop-discuss@w3.org, (bcc: Jos 
>         Subject:        Re: log:notIncludes (conclusion?)
> > I think the key is that semantics(+URL,-Formula) predicate and the fact
> > that you are leaving out of the picture the actual formulas that are
> > sitting at URL. The formula that you are getting using semantics/2 is 
> (as I
> > understand) a list of terms that reify logical statements.
> > 
> > So, you have
> > 
> > formulas sitting at URL  (*)
> > the built-in semantics(URL,Formula)
> > and then you have something like
> >     Formula notIncludes somelist
> > 
> > So, adding a new formula to the set (*) can change the list Formula
> > and invalidate a previously true statement of the form
> > Formula notIncludes somelist.
> Yes.  I think we're understanding each other very well, now.
> > This is nonmonotonic.
> I'm not sure I know the right words for this, but that stuff sitting
> at that URL is considered immutable within one inference run.  cwm
> makes no attempt to read it more than once; any change in it would go
> along with an overall change in the state of the world.  A
> long-running N3-based agent would have to start everything over each
> delta-t (or cleverly act like it did).  Each time something observable
> about the universe changes, we're talking about a new set of models
> and interpretations.
> Going back to the definition of monotonicity you and DanC were using
> [1], the stuff sitting at that URL isn't part of A or B.  Nothing is
> entailed by that stuff at the URL.  To be slightly silly, adding a
> formula to it is no more relevant to the notion of monotonicity than
> is adding characters to the end of some constant symbol in an FOL
> formula.
> Now, am I sounding confused again or like this is a sensible design
> (even if not the one you might chose)....? 
>       -- sandro
> [1] http://lists.w3.org/Archives/Public/public-rule-workshop-discuss/2005Aug/0072
Received on Saturday, 27 August 2005 20:22:10 UTC

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