W3C home > Mailing lists > Public > semantic-web@w3.org > July 2010

Re: Subjects as Literals

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 6 Jul 2010 16:17:38 -0500
Cc: Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-Id: <A56CA316-41C8-4310-A90F-89E4F367BFC8@ihmc.us>
To: Henry Story <henry.story@gmail.com>

On Jul 6, 2010, at 1:45 PM, Henry Story wrote:

>
> On 6 Jul 2010, at 14:03, Michael Schneider wrote:
>
>> Toby Inkster:
>>
>>> On Mon, 5 Jul 2010 17:43:17 -0500
>>> Pat Hayes <phayes@ihmc.us> wrote:
>>>
>>>> Well, nobody is suggesting allowing literals as predicates  
>>>> (although
>>>> in fact the RDF semantics would easily extend to this usage, if
>>>> required, and the analogous structures are allowed, and do have
>>>> genuine use cases, in ISO Common Logic.)
>>>
>>> Actually, I have suggested allowing them just to make things  
>>> simpler -
>>> URIs, blank nodes and literals would all be allowed in any position.
>>> However, a statement with a literal in the predicate position  
>>> would be
>>> officially defined to have no meaning.
>>
>> So, if
>>
>>   :s "lit" :o .
>>
>> must not have a semantic meaning, what about
>>
>>   "lit" rdf:type rdf:Property .
>
> This would be possible to say. The problem is that there would be no
> way on earth that anyone could come to an agreement as to what kind
> of property "lit" was. Everyone could make up defend their choice. And
> where there is no right or wrong, there is no meaning. Hence the above
> is undecidable.

True (though you use "undecideable" here not in its technical sense, I  
presume) but the same is true for any RDF at all.

>
> What is the difference between the above and
>
>   foaf:knows a rdf:Property .
>
> Well we can dereference foaf:knows to find out what it means.

Not according to the RDF specs, you can't. That is, you can (maybe)  
dereference it, but what you get has no bearing upon its (official)  
meaning. Maybe it should, but that idea needs a LOT of work to get  
straight. It is one proposal in the RDF2 wish-list, in fact.

> This is
> the canonical way to find it's meaning, and is the initial procedure  
> we
> should use to arbitrate between competing understandings of its  
> meaning.

Whoo, I doubt if that idea is going to fly. I sincerely hope not.  
Using that, how would you determine the meaning of the DC vocabulary?

Pat


>
> 	Henry
>
>

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Received on Tuesday, 6 July 2010 21:18:38 UTC

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