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Re: Contradicting definitions of “property”

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 23 Aug 2012 00:55:18 -0500
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, RDF Working Group WG <public-rdf-wg@w3.org>, Simon Reinhardt <simon.reinhardt@koeln.de>
Message-Id: <DFD67F3F-6AE7-4B2B-92B5-16BFB614F4B9@ihmc.us>
To: Richard Cyganiak <richard@cyganiak.de>

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. 

> 
>> 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. 

> 
> 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. :-)

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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Received on Thursday, 23 August 2012 05:55:53 UTC

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