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Re: REQDOC: reification

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Fri, 15 Feb 2002 20:11:31 -0500
Message-Id: <p0510145db89360cf7510@[192.168.0.6]>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: webont <www-webont-wg@w3.org>
>From: Pat Hayes <phayes@ai.uwf.edu>
>Subject: Re: REQDOC: reification
>Date: Fri, 15 Feb 2002 01:11:08 -0500
>
>>  >One of the requirements in the requirements document is the ability to
>>  >associate properties with statements.  This would require, at least,
>>  >some version of reification of statements, and to work right would require
>>  >a way of referring to statings.
>>  >
>>  >RDF has made a total hash of reification.
>>
>>  I don't agree. RDF certainly screwed up in some ways. It is
>>  incomplete, and the M&S is confused and ambivalent between divergent
>>  readings, but the general idea is sound, if rather simple, and the
>>  use cases that we have been able to discover all pretty much converge
>>  on one of the two plausible readings of the M&S wording, so the WG
>>  will probably give a reasonably clear ruling on this soon. So its not
>>  a total hash. It is pretty useless, in my view, but some people can
>>  use it coherently and seem happy with it.
>
>Well, there is a document (RDF M&S) that says one thing (every statement
>has exactly one reification), is often read as another (there can be
>any number of reifications for a statement), and is used in a third way (a
>reified statement corresponds to a stating).  What else can this be but a
>hash?

Oh, the *documentation* is a hash, sure. But that's what the WG is 
doing, sorting out the confusion. It turns out that virtually all 
case uses in fact interpret reification in one way. So the WG is 
going to say that that's what it means, and its a simple, clear 
meaning that provides a simple, basic functionality. Nothing fancy, 
but thats OK.

>  > >The RDF Core WG is trying to fix
>>  >this a bit, but it is probably out of their scope to make any significant
>>  >improvment (as opposed to significant fix).
>>  >
>>  >I think that adding reification to OWL would be, at best, a significant
>>  >research project and, at worst, a black hole.
>>
>>  I think that what might be called simple object reification - the
>>  ability to describe syntactic object tokens, including those of the
>>  language itself, and some kind of external referential linking
>>  mechanism analogous to ostensive pointing to an expression token - is
>>  quite do-able, raises no deep black-hole issues (notice I carefully
>>  did not say 'tr*th pre*d*c*te' ) and provides about 90% of the
>>  practical functionality needed by enthusiasts of reification. So I
>>  think that something useful can be done pretty easily. It will be
>>  moderately trivial from a FOM perspective, for which we should all
>>  breath sighs of relief.
>
>Well, yes, if all you want is some syntax (rdf:Statement, rdf:subject,
>rdf:predicate, rdf:object) that has no other meaning, then go ahead.  I
>would say this gets about 0% of the practical functionality of reification
>with about 0% of the effort.

No, it gets about 95% of the practical functionality with 5% of the 
effort, which is a pretty good deal.  People use it for tagging, 
basically. Maybe calling it 'reification' was overambitious, and 
certainly all that stuff in the M&S about indirect speech acts was 
totally off the wall. BUt that's just a matter of good technical 
writing.

>  If users of RDF want to use the non-existent
>functionality of this syntax to hang any outside-of-RDF reification onto
>then they can.   But why then make all this part of RDF?  You aren't
>getting anything for it from RDF (except, maybe, a gentleman's agreement to
>use the same URIs).

Quite. But such agreements are often all that people want. Logically 
trivial, generally useful: a perfect combination.

>
>>  >In any case, I don't see the motivation for the ability to associate
>>  >properties with statements (in the OWL logic, at least) from the shared
>>  >ontologies goal.  Surely it is possible to share ontologies without
>>  >associating properties with statements.
>>
>>  The real use case is associating them with statings, ie *tokens* of
>>  expressions in ontology documents. And that is needed in for example
>  > date-stamping, tracking provenances, that kind of thing.
>
>Yes, sure, but how does RDF reification help in this?  Futher, this is not
>a ``sharing ontologies'' motivation any longer.

Its connected, since these provenance issues come up whenever you 
want to refer to ontologies. Hey, its not rocket science, I agree. 
BUt be grateful for small mercies.

Pat
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Received on Friday, 15 February 2002 20:11:29 GMT

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