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Re: RDF-ISSUE-25 (Deprecate Reification)

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 11 Apr 2011 13:50:35 -0500
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <AF681DA9-C4D5-4EC2-AF22-C6D9AA96761B@ihmc.us>
To: Sandro Hawke <sandro@w3.org>

On Apr 11, 2011, at 12:15 PM, Sandro Hawke wrote:

> On Mon, 2011-04-11 at 12:01 -0500, Pat Hayes wrote:
>> More...
>> 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. 
> Sorry, I still don't see a bright line there (between this and
> reification).  

I guess I give up at this point, Sandro. If you can't see the difference between making assertions about the (or a) world, and making assertions about syntax, I don't think we are going to be able to communicate rationally. To me, these are about as different as two things can be. Ever noticed what the original meaning of 'ontology' is?

>  This could have been about unicorns and fairies.  And it
> could be something that's debatable or even false about unicorns and
> fairies.  This is, as I see it, this is just a statement.   
> <Sandro> :doesNotBelieve [ 
>    :ternaryRelation eg:favoriteRidingWeather,
>    :op1 eg:elves,
>    :op2 eg:unicorns,
>    :op3 eg:rain ]
> That is: Sandro does not believe that for elves, rain is the best
> weather in which to ride a unicorn.

Fine, if there are unicorns in your world, go ahead. But still, you won't want to get unicorns and syntax confused, I reckon. Or at any rate, if you do, then you are just contributing to the global confusion about what all this linked data is supposed to be about.


>   -- Sandro
>> Pat
>>> 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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IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Monday, 11 April 2011 18:51:07 UTC

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