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Re: Contradicting definitions of “property”

From: Richard Cyganiak <richard@cyganiak.de>
Date: Wed, 22 Aug 2012 22:58:45 +0100
Cc: RDF Working Group WG <public-rdf-wg@w3.org>, Simon Reinhardt <simon.reinhardt@koeln.de>
Message-Id: <7CDDF6B7-6283-4705-AA24-681B76C0408D@cyganiak.de>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
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.


> 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?

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"?

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."

Or: "The predicate IRI denotes a property, that is, a resource that can be formalized as a binary relation."

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?


> [1] 1.2 Resources and Statements. http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#resources-and-statements
Received on Wednesday, 22 August 2012 21:59:15 UTC

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