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Re: Contradicting definitions of “property”

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Thu, 23 Aug 2012 12:25:46 +0200
Message-ID: <5036052A.7090102@emse.fr>
To: Pat Hayes <phayes@ihmc.us>
CC: Richard Cyganiak <richard@cyganiak.de>, RDF Working Group WG <public-rdf-wg@w3.org>, Simon Reinhardt <simon.reinhardt@koeln.de>

Le 23/08/2012 07:55, Pat Hayes a écrit :
>
> On Aug 22, 2012, at 4:58 PM, Richard Cyganiak wrote:
>
>> On 13 Aug 2012, at 18:29, Antoine Zimmermann wrote:
>>>> Note that the new Introduction section in the RDF Concepts ED
>>>> contains an *informative* sentence that introduces the term
>>>> “property” [4], and it is in line with RDF Semantics:
>>>>
>>>> [[ The predicate itself is an IRI and denotes a binary
>>>> relation, also known as a property. ]]
>>>
>>> This is not what the RDF semantics says. A predicate denotes a
>>> resource that must be in IP, the set of properties in the
>>> interpretation. Resources in IP are associated with a binary
>>> relation via the extension function IEXT. This is an important
>>> distinction since this is what allows RDF to talk about
>>> properties, classes, etc as instances.
>>
>> Ah, right. I forgot about the class/property extension stuff in RDF
>> Semantics.
>>
>>> If predicates were denoting binary relations, the following would
>>> be RDFS-inconsistent, when it is, in fact, RDFS-consistent:
>>>
>>> :p  rdf:type  xsd:string . :s  :p  :o .
>>
>> Do I get this right? This would be inconsistent because the first
>> triple says its a Unicode string, and the second triple entails
>> that it is a property, and hence (if my phrasing above were indeed
>> correct) a binary relation. And a Unicode string is not a binary
>> relation.
>>
>> And in reality, as RDF Semantics defines things, the second triple
>> only entails that the Unicode string *has a property extension*,
>> and the property extension is a binary relation. Hence, no
>> contradiction. Anything can have a property extension.
>>
>> Right?
>
> Right. In RDF, in fact, everything *does* have a property extension
> (whether you are using it or not, it is there to be used.) In this it
> follows ISO Common Logic, by the way.

Nope. From RDF Semantics 2004, Section 1.3:

"3. A mapping IEXT from IP into the powerset of IR x IR i.e. the set of 
sets of pairs <x,y> with x and y in IR ."

only elements of IP, aka properties, have a property extension.


>
>>
>>> This is a proposal to replace the wording in section 1.2 [1]:
>>>
>>> "The predicate itself is an IRI and denotes a property, that is,
>>> a resource that defines a binary relation."
>>
>> As usual, given that this is informative introduction text, there
>> is a balance to be found between accuracy and simplicity. So I'd
>> like to toss this around a bit.
>>
>> Is it accurate to say that the resource "defines" a binary
>> relation? In what sense does it do that?
>
> Good point.
>
>>
>> Wouldn't it be slightly more accurate (but perhaps less
>> understandable) to say that the predicate IRI denotes "a property,
>> that is, a resource that can be interpreted as a binary relation"?
>
> Yes. Or more accurately still, "...which is being interpreted as
> a...." .
>
>>
>> How about the fuzzy but perhaps simpler: "The predicate IRI denotes
>> a property, that is, a resource that can be thought of as a binary
>> relation."
>
> Better, I agree.

Good, I agree with this too.

>
>>
>> Or: "The predicate IRI denotes a property, that is, a resource that
>> can be formalized as a binary relation."
>
> Nah, that suggest a misleading direction to push intuitions. I like
> the previous idea.
>
>>
>> I note that the overall purpose of the sentence is just to
>> introduce the term "property" and give readers a decent intuition
>> of what the term means. From that point of view, I still quite like
>> the current phrasing ("The predicate IRI denotes a binary relation,
>> also known as a property.") even though I know it's technically
>> inaccurate. May I claim "harmless abuse of terminology" here?
>
> I think you can, yes. After all, people *can* read the actual
> semantics if they want to get the details absolutely right. :-)

Yes, but I like the fact that RDF Concepts explains what the concepts 
actually means such that it reduces the need to refer to the semantics. 
RDF Concepts 2004 was missing a bit in that respect.


AZ.


>
> Pat
>
>>
>> Best, Richard
>>
>>
>>> [1] 1.2 Resources and Statements.
>>> http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#resources-and-statements
>>
>>
>
>>>
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>
>
>
>

-- 
Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
42023 Saint-Étienne Cedex 2
France
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Received on Thursday, 23 August 2012 10:26:12 UTC

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