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Re: [SKOS, SPARQL, ALL] Closure and SPARQL

From: David Wood <dwood@softwarememetics.com>
Date: Mon, 12 Dec 2005 09:00:53 -0500
Message-Id: <7EFB77CB-D848-42FF-94F1-1EE9FAAAD58C@softwarememetics.com>
Cc: "Christoffel Dhaen" <christoffel@landcglobal.com>, "Enrico Franconi" <franconi@inf.unibz.it>, "Pat Hayes" <phayes@ihmc.us>, "Christopher Welty" <welty@us.ibm.com>, <public-swbp-wg@w3.org>
To: "McBride, Brian" <brian.mcbride@hp.com>

On 12 Dec2005, at 03:10, McBride, Brian wrote:
> I take it you are speaking as a member of the WG rather than as a  
> chair
> here.

Absolutely right.  I was definitely NOT speaking as co-chair.

> I note also that you have raised this issue but have not responed
> to my other comment on SPARQl concerning DESCRIBE.

Hmm, yes.  Sorry about that.

> It might  be useful background for the WG David, if you would explain
> why you feel this issue is important.

I have found in practice (empirically, with Kowari/Tucana, lots of  
mostly government data and watching the kind of queries which become  
necessary to solve real-world problems) that transitive closure over  
RDF graphs is needed.  Just because this statement is based upon  
empirical evidence not currently grounded in a good theory does not  
make it wrong.  In fact, I might even be tempted to place it in a  
"best practice" category.

...
> I do not understand your reference to "non-standard" mechanisms which
> seems like a bit of unwarrented sophistry.  I don't see the argument,
> grounded in SWBP work, for introducing an optional element to the
> language as this will introduce interoperability issues.

I would /personally/ prefer to have a SPARQL which defines an  
optional mechanism to handle transitive closure than to have a SPARQL  
which defines no way of doing it at all.  An optional mechanism  
relieves any implementor from providing it, but ensures that those  
who find they need it do it in the same way.

...
> I am also not clear what you are asking for here.  Christoffel's  
> message
> seems to suggest that he is just asking for RDFS semantics, i.e. the
> transitive closure of subPropertyOf and subClassOf.  He also mentions
> domain and range.  Your text mentions transitive closure in  
> general, as
> opposed to just closure on RDFS properties, but makes no mention of
> other inferred triples, e.g. from domain and range constraints, other
> Owl constructs, or indeed inferred by any means e.g. rules.  What
> exactly do you want and why?

I think it is reasonable to recognize that SPARQL is unlikely to  
change a great deal between now and Recommendation status.  I limited  
my suggestion for a WG position to one with minimal impact on the  
DAWG's current draft.

> In short, Christoffel's position reads to me like "I wouldn't do it  
> that
> way", which is fine - I might not do it that way either - but I am
> suggesting that the WG should set a higher burden on itself before
> commenting on the work of other working groups.  Every comment has a
> cost, and we should take care that cost we impose on other WG's is
> justified.  It is appropriate for other WGs to say "this gives us a
> problem because" or "this violates one of our specs", but I don't  
> think
> it is appropriate to duplicate the work of another WG with comments of
> the form "I woudn't do it that way".

That is very valid and I concur.  I have posted some thoughts on SWBP  
work affected by SPARQL's current state and, although there were some  
problems with that initial post, I am still waiting on consensus to  
arise.  Clearly, a WG position cannot be taken without one.  That  
doesn't stop us from periodically reining in the discussion and  
proposing a position to see what the reaction might be.  That is what  
I did.

Regards,
Dave
Received on Monday, 12 December 2005 14:01:37 UTC

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