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Re: RDF-ISSUE-25 (Deprecate Reification): Should we deprecate (RDF 2004) reification? [Cleanup tasks]

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 9 Apr 2011 08:49:56 -0500
Cc: Richard Cyganiak <richard@cyganiak.de>, Ivan Herman <ivan@w3.org>, RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <59B2943D-1AF3-4E47-9EF0-A068CAB0C6D8@ihmc.us>
To: William Waites <ww@styx.org>

On Apr 9, 2011, at 7:28 AM, William Waites wrote:

> * [2011-04-09 13:09:15 +0100] Richard Cyganiak <richard@cyganiak.de> écrit:
> ] 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. 

> Whilst I support this, I think the distinction between *statements*
> and *relationships* is highly artificial. A statement is just a binary
> relationship.

WRONG! A relationship is, well, a relationship. Formally, it is a set of pairs of things. A statement is something that asserts that a relationship holds between some things (or it can be more complicated, of course). The statement that, say, PatHayes owns 121HIghPinesPlace asserts that the relationship *owns* holds between the pair of things <PatHayes, 121HIghPinesPlace>. The statement uses a relationship name and mentions the relationship, but it is not the same thing as the relationship. 

> The only reason the number 2 is special and the reason
> that RDF is not prolog, is because it is the smallest arity in which
> you can expres arbitrary arity relations *if you use reification*.

No, it is special because it is the smallest arity in which you can express arbitrary relationships if you can share names between atomic sentences, so you can say things like a R1 b & b R2 c & c R3 d ... or like a R1 b & a R2 c & a R3 d ...  Either pattern (and others) can be used. But none of this has anything to do with reification. (BTW, if you restrict things so that you can only share a name once then you need triadic relations, which Pierce in around 1880 thought was terribly significant: trinities and all that.)


> Because 2 is special we have a special vocabulary for dealing with it,
> but that turns out not to be especially useful because there's direct
> support in the language for it, and the remaining use for it,
> provenance, we have better ways of handling.
> Cheers,
> -w
> -- 
> William Waites                <mailto:ww@styx.org>
> http://river.styx.org/ww/        <sip:ww@styx.org>
> F4B3 39BF E775 CF42 0BAB  3DF0 BE40 A6DF B06F FD45

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Received on Saturday, 9 April 2011 13:50:51 UTC

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