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Re: Handling multiple rdfs:ranges

From: Reto Gmür <reto@wymiwyg.com>
Date: Fri, 26 Feb 2016 17:14:10 +0100
Message-Id: <1456503250.704819.532822770.65D14647@webmail.messagingengine.com>
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>, Pat Hayes <phayes@ihmc.us>
Cc: semantic-web@w3.org
On Fri, Feb 26, 2016, at 14:28, Peter F. Patel-Schneider wrote:
> On 02/26/2016 01:52 AM, Reto Gmür wrote:
> > 
> > On Thu, Feb 25, 2016, at 06:18, Pat Hayes wrote:
> >>
> >> On Feb 23, 2016, at 10:24 AM, Reto Gmür <reto@wymiwyg.com> wrote:
> >>
> >>> On Tue, Feb 23, 2016, at 17:05, Peter F. Patel-Schneider wrote:
> >>>> On 02/23/2016 07:31 AM, Reto Gmür wrote:
> >>>>> [...]
> >>>>>
> >>>>> Granted, the semantics of :rangeIncludes are very weak (under OWA) but
> >>>>> the fact that you can create contradictions with it shows that it's not
> >>>>> completely meaningless.
> >>>>>
> >>>>> ex:prop1 s:rangeIncludes :Cat .
> >>>>> :Cat owl:disjointWith :Dog .
> >>>>> ex:prop1 owl:range :Dog .
> >>>>>
> >>>>> The above graph evaluates to false in every possible world, this is not
> >>>>> the case if you omit any of the 3 triples, this shows that
> >>>>> `s:rangeIncludes` is not a meaningless decoration.
> >>>>>
> >>>>> Reto
> >>>>
> >>>> I don't think that this follows from the semantics of :rangeIncludes,
> >>>> even if
> >>>> you augment schema.org semantics with disjointness.
> >>>
> >>> In the example I also used "owl:range" to create what I thought is a
> >>> contradiction.
> >>>>
> >>>> Perhaps one could also count the documentation of
> >>>> rangeIncludes as authoritative as well.  So from
> >>>> https://schema.org/rangeIncludes, rangeIncludes "[r]elates a property to
> >>>> a
> >>>> class that constitutes (one of) the expected type(s) for values of the
> >>>> property" would also be part of the semantics of schema.org ranges.
> >>>
> >>> I considered only this definition. And based on that I still think there
> >>> is a contradiction, if the owl:range of a property excludes :Cat (which
> >>> is expressed with the statements using owl-properties), :Cat cannot at
> >>> the same time "be (one of) the expected type(s) for values of the
> >>> property".
> >>
> >> Of course it can. It only follows that the values of this particular
> >> property are all in some other part of the range. According to the
> >> schema.org definition of rangeIncludes, this is quite permissible. 
> > 
> > I'm not getting you.
> > 
> > from
> > 
> > (1) :Cat owl:disjointWith :Dog .
> > (2) ex:prop1 rdfs:range :Dog .
> > 
> > It follows that: (3) "no value of the property ex:prop1 can be an of
> > type :Cat".
> > 
> > Do we agree till here?
> > 
> > (4) ex:prop1 s:rangeIncludes :Cat 
> > 
> > means: (5) "The class :Cat is an expected type for values of the
> > property ex:prop1"
> > 
> > Do you agree that (5) follows from (4) when using the definition from
> > http://schema.org/rangeIncludes?
> 
> No.  This sentence reads as if each expected type for a property is the
> type
> of all values of the property.  This is not the case at all in
> schema.org.
> 
> Even the slightly weaker statement at https://schema.org/rangeIncludes is
> not
> suitable.  The wording there "Relates a property to a class that
> constitutes
> (one of) the expected type(s) for values of the property." also reads as
> if
> each expected type is supposed to be a type of all values of the
> property.
> 
> > Agreeing to both (4) and (5) boils down to:
> > 
> >  - :cat is an impossible type for values of the property ex:prop1
> >  - :cat is an expected type for values of the property ex:prop1
> 
> Not exactly.  "Impossible" is a very strong word here, even stronger than
> contradictory.  It is certainly possible for a value of a property to
> have a
> type that contradicts the range of the property.  It just triggers a
> contradiction (or maybe even something with even less import), which does
> what
> contradictions (or whatever) do in the setup one is currently working in.

Doesn't "p rdfs:range t" mean that it is *necessary* for all objects of
p to be of type t? If so by modal logic it is *impossible* for an object
of p not to be of type t.

In how far do you see impossible as stronger than contradictory? If I
ask why something is impossible I'm happy with an answer that proofs
that it would contradict itself or one of the axioms. What more do you
need for impossibility?


> 
> > Using the first definition of "Expect" from the oxford dictionary as
> > "Regard (something) as likely to happen", I think there is a
> > contradiction between asserting that something is impossible and that
> > something is expected.
> 
> Certainly there would be something odd going on in an extended schema.org
> setup if one of the rangeIncludes of a property were disjoint from a true
> range of the property.  I do not, however, believe that this oddness is
> anything near a strong contradiction (i.e., something that causes all
> information to be meaningless).

I think that for any charitable interpretation of
https://schema.org/rangeIncludes for "p schema:rangeIncludes t" to hold 
it must be  *possible* for an object of p to be of type t. 

Of course being "likely" means more than being "possible" but the former
implies the latter and possibility is all that is needed to create a
contradiction with statements of necessity and negation.


Reto
> 
> > 
> > I would really like to learn where you think my reasoning is wrong.
> > 
> > Cheers,
> > Reto
> >  
> >> If you disagree, please suggest how to express the schema semantics as a
> >> precise model-theoretic condition in such a way that it produces the
> >> contradiction you expect. 
> >>
> >> Pat Hayes
> >>
> >>>
> >>> Reto
> 
> peter
> 
Received on Friday, 26 February 2016 16:14:35 UTC

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