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Re: Concerns about reification

From: Frank Manola <fmanola@mitre.org>
Date: Tue, 19 Feb 2002 14:33:31 -0500
Message-ID: <3C72A88B.5B484073@mitre.org>
To: Brian McBride <bwm@hplb.hpl.hp.com>
CC: Sergey Melnik <melnik@db.stanford.edu>, RDFCore WG <w3c-rdfcore-wg@w3.org>
Brian, Sergey--

Let me to refer you to: 
http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0452.html 
(my earlier reply to Sergey's post)

and to:
http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0449.html
http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0459.html
http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0462.html
(discussion with Ron Daniel about his provenance use case, and the value
of having the reification vocabulary)

I think that:

a.  There *is* value in having the vocabulary
b.  We can assign useful meaning to the terms in that vocabulary
c.  The vocabulary by itself doesn't do what you want "reification" to
do for the uses described for it in the M&S.  I don't see how a decision
for "statement" rather than "stating" changes all that much about the
definition of the reification vocabulary.  Even more, I don't see what
good it does to be able to interoperate via this vocabulary if the use
of that vocabulary doesn't allow you to express what you (presumably)
want the applications to interoperate about.  Is there some major use
case other than provenance that we don't know about?

Brian says:
> I have not officially closed the issue, though I plan to put it
> up for closure this week, if Frank agrees that is appropriate.

I think it's probably appropriate to ask if people think we've done
enough or, at least, what else they think ought to be done to "declare
victory".  My own view (expressed in my message to Sergey) is that we
can't just "wash our hands";  too much has been made of "RDF
reification" in the past.  That means we probably need to be more
explicit about what our "revised position" is about reification, e.g.,
for guidance of any editor that needs to write about it.  (In other
words, here's an invitation for anyone who wants to "declare victory" to
write the "victory declaration statement".)

--Frank
 

Brian McBride wrote:
> 
> Hi Sergey,
> 
> At 10:11 15/02/2002 -0800, Sergey Melnik wrote:
> >Brian asked me (for the Xth time, sigh) to express my concerns about
> >reification in writing. My position remains that we need an
> >interoperable and efficient way of doing reification.
> 
> I'm sorry about the repeats.
> 
> >If we go for "stating" (answer "No" to Q1 in [1]), no special semantics
> >is associated with the vocabulary rdf:Statement, rdf:subject,
> >rdf:predicate and rdf:object. This means applications *cannot
> >interoperate* using this vocabulary since its meaning is unspecified.
> >Effectively, going for "stating" amounts to deprecating 4-triple
> >reification as used today.
> 
> I see what you mean here, and I agree with it, though I think you express
> it a bit too forcefully.  There was no model theory in M&S at all, but
> folks seem to have managed to do useful things with it.  Thus, even without
> model theoretic semantics, the reification vocabulary can be used, and
> provided you understand the semantics attached to it by a particular
> application, then you can do useful things with it.
> 
> But I agree with you, that it defines no semantics that apply across the
> board to all applications.
> 
> >If we go for "statement" (answer "Yes" to Q1 in [1]), we get a (rather
> >painful, admittedly, but endorsed) way of referring to statements found
> >on Web pages and in RDF databases, recording provenance etc. This is IMO
> >much more concrete and useful that just providing no definition at all,
> >although the usability of 4-triple reification still remains seriosly
> >hampered by its verbosity.
> >
> >In summary, if we go for "stating" we have *no* official mechanism for
> >reification. In this case we'd have to suggest an alternative, we cannot
> >just wash our hands. It is an illusion that we can leave the vocabulary
> >undefined and at the same time recommend developers to use it in a
> >consistent way. If we go for "statement" we do have a solution, albeit a
> >poor one. If we run out of time in finding an alternative *efficient*
> >way of doing reification, we could of course fall back on "statement"
> >expressed using 4 triples. In this case, we would not have achieved much
> >since inefficiency proved to be a show stopper for using 4-triple
> >reification in the past 3 years.
> 
> We have run out of time.  However, there has been talk on this list of some
> folks getting together and proposing new vocabulary, possibly publishing as
> a note.  That could be a way forward.
> 
> There has been strong support in the WG for the position we have now
> reached.  I have not officially closed the issue, though I plan to put it
> up for closure this week, if Frank agrees that is appropriate.
> 
> Brian

-- 
Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-8752
Received on Tuesday, 19 February 2002 14:38:33 EST

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