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Re: Reification - whats best practice?

From: Frank Manola <fmanola@acm.org>
Date: Sat, 28 Aug 2004 18:00:19 -0400
Message-ID: <41310073.1@acm.org>
To: Bob MacGregor <macgregor@isi.edu>
CC: www-rdf-interest@w3.org


I'm taking this off-list after this response.

Bob MacGregor wrote:

> Hi Frank,
> I don't want to have too many comments on comments, but at least one of 
> your points needs
> clarification.  Not only do I not blame Pat Hayes for the state of 
> reification in RDF, I applaud
> him.  

Good.  The point about Pat's contribution (whose ever it was) is now 

> You mention the possibility that if we admit "named containers" 
> (contexts) to RDF then we open
> the possibility of people representing provenance information in more 
> than one way.  

Not just "more than one way" (as you note, we can already do that) but, 
by introducing yet another basic mechanism, we introduce another 
*collection* of "more than one way"s.

There are
> two major objections to that position.  One is that its impossible to 
> prevent that possibility -- we
> are dealing with logic, and any logic that has sufficient expressivity 
> for practical application will
> admit more than one way of solving a given technical problem.  RDF's 
> lack of semantics makes
> it in some sense very expressive.  I am already expressing provenance 
> information in RDF; and
> the way I do it is certainly not approved by the RDF spec.  In fact, its not
> approved by me -- I could have done it the "right" way by embedding 
> reified statements in a
> named container, but that would have had horrendous space implications, 
> and been impossible
> from a querying point of view.  Instead, I invented a "hack" that gives 
> the right behavior, but
> would never be recommended as an official way to do contexts.  So, by 
> necessity, I'm doing
> exactly what you are counseling we shouldn't be doing.

Why do you think I'm counseling you not to do what you need to do (and 
why do you think it would never be recommended)?  As the mail on the 
subject suggests, we have lots of people trying different approaches. 
Just below, you say that experimentation with various kinds of 
provenance representations would be "ideal".  Isn't that what people are 
doing?  What's wrong with the "figuring out which is best" step then?

> The second objection to your position is the chicken-and-egg problem.  
> Ideally, we could
> experiment with various kinds of provenance representations, figure out 
> which is the best,
> and then make that a standard.  However, the gap between what's needed 
> is too large
> to admit experiements within the RDF framework.  Think about the 
> relational database
> community.  They have gone more than 25 years without a decent solution 
> to representing
> provenance information.  Why? because their representation doesn't admit 
> a good solution.
> Unfortunately, RDF is in nearly as bad a state right now -- not quite as 
> bad, because the
> hack that I use would not be practical within the relational model -- 
> but bad enough.  So
> we are in a position that the only people that can experiment with 
> provenance are those
> willing to violate the RDF spec.

Can you point me to further information on the relational database 
community lacking a decent solution to representing provenance 
information (i.e., I can imagine at least one reason why it might be a 
problem, but I'd like to know what specifically you're referring to)?

> But its actually worse than that.  To get decent performance while using 
> provenance,
> you have to make modifications at the implementation level.  Relatively 
> few users are going
> to build or extend an existing triple store just to get provenance 
> information.  So, the
> "experiment" is going to proceed relatively slowly.  On the other hand, 
> suppose Jena
> implemented quads.  Suddenly, the opportunities for experimentation 
> would increase
> 100-fold (to pick a random number).  Then there would be a flurry of 
> experimentation,
> probably leading to much earlier recognition of what a standard 
> semantics for
> provenance (a step beyond contexts) should look like.

Sorry, but I didn't understand your argument as being that one or more 
implementations should provide quads.  I'd certainly be happy to see 
them do that (assuming they don't already), but surely they can do that 
entirely on their own, without having everyone adopt a new container 
mechanism, can't they?

> Right now, the people adopting your position are consigning the majority 
> to a
> Gedankenexperiment, where the expected rate of progress will be about 
> what it
> is in the relational database community -- nil.

I hadn't realized that "the people adopting my position" had so much 
power (I hadn't realized there was more than just me either!) that they 
could prevent the majority from doing whatever it wanted to do.  If 
that's really the case, then all I can say is, "let them eat contexts" 
(I'll be around with a basin and a wet mop as soon as I can).

> Cheers, Bob


Received on Saturday, 28 August 2004 21:57:37 UTC

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