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Re: RDF-ISSUE-25 (Deprecate Reification)

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 11 Apr 2011 12:01:06 -0500
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <D3BF7C27-99AD-42D8-ABB1-700A0E59B3E2@ihmc.us>
To: Sandro Hawke <sandro@w3.org>

On Apr 10, 2011, at 11:50 PM, Sandro Hawke wrote:

> On Sat, 2011-04-09 at 08:49 -0500, Pat Hayes wrote:
>>> ] ISSUE-25 is about the RDF reification vocabulary, which is a
>>> ] built-in vocabulary for reifying *statements*. You are talking 
>>> ] about a common modeling practice in domain vocabularies for
>>> ] reifying *relationships*. That has nothing to do with ISSUE-25.
>>> Right, that was what I wanted to have explicitly clear. It's not the
>>> idea or practice of reification that is to be deprecated but the
>>> baked-in support for reifying binary relations.
>> No, really, you have this wrong. It IS the idea of reification that is
>> being deprecated; and this device that you have mentioned, of encoding
>> an n-ary relation using a bundle of binary 'role' relations, is NOT
>> reification. The two things are distinct. Using the name of one to
>> refer to the other is going to cause a lot of confusion. Reification
>> is using RDF to *describe* other pieces of RDF. 
> Pat, I'm a little confused here.   What I think William is saying sounds
> right to me, so I don't know why you're calling it wrong.
> If we have ternary relationship "showing", between a movie, a show-time,
> and a theater, and we want to represent that in RDF, we have (as you've
> both pointed out) several options.   If we have a lot of similar ternary
> relations, we might choose a  generalized representation like this:
> [ :ternaryRelation movie:showing;
>   :op1 "The Sound of Music";
>   :op2 "2011-04-11T12:40:00Z"^^xs:datetime;
>   :op3 eg:SomeTheater ]

But that would be a terrible way to express it. Ask yourself: what is this 'thing' whose existence is being asserted and is the subject of these triples? It really is not a *relation*, ternary or otherwise. I mean, the *relation* itself would exist (or, if you are of a nominalist persuasion, not exist) independently of the mere facts of some movie being shown somewhere. Maybe you could say that it is an *instance* of a ternary relation, but even that is an odd way to express oneself.  What it is, surely, is a fact or event or circumstance (or situation or occurrent or... ) *in the actual world*, the showing of this movie at this time in this theatre. It has a time and a place, it uses energy and might have legal consequences, this thing. It is **real**.  And it  this movie-showing-event-thingie  has a bunch of properties, which these handily binary relations can express in RDF. The point being, that this is a substantive factual assertion about real things in the actual world; it is not a Platonic abstract assertion about things like relations or RDF triples or other syntactic objects. 


> We could of course do something similar for any particular arity
> relation.   If we did it for the 2-ary case it would look exactly like
> 2004 RDF reification, wouldn't it?
> Now, William's example [1] was more like:
> [ a movie:Showing;
>   movie:title "The Sound of Music";
>   movie:showtime "2011-04-11T12:40:00Z"^^xs:datetime;
>   movie:theater eg:SomeTheater;
> ]
> ... but the difference between my two examples doesn't seem to me to
> cross a bright line, where the first is the evil reification and the
> second is recommended practice.  If you see a bright line there, could
> you try to make it more clear for me what exactly it forbids?   Thanks.
>     -- Sandro
> [1] http://lists.w3.org/Archives/Public/public-rdf-wg/2011Apr/0232.html

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Received on Monday, 11 April 2011 17:01:35 UTC

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