Re: Non-PK tables, blank nodes, and leanness

On Tue, Apr 24, 2012 at 11:11 PM, Enrico Franconi <franconi@inf.unibz.it>wrote:

> Nope, there is no mismatch.
> SPARQL just doesn't give a *minimal* answer, since it would be
> too expensive.
>

True


> In other words, SPARQL may give different (but equivalent) answers to
> equivalent graphs.
>

I disagree. If you compute the core (the result of removing redundant blank
nodes aka lean rdf graph),  you get same answers. But if you dont compute
it, you get different answers.

For example:

ASK{
?x <IOU#BORROWER> "Alice".
  ?x <IOU#AMOUNT> 10.
 ?y <IOU#BORROWER> "Alice".
  ?y <IOU#AMOUNT> 10.
FILTER (?x != ?y)
}

Will return true on a non lean rdf graph (per the example below) and would
return false on a lean rdf graph

on the le


> Check out my PODS-2006 invited talk slides at
> <http://www.inf.unibz.it/~franconi/papers/franconi-slides-pods-2006.pdf>.
> cheers
> --e.
>
> On 24 Apr 2012, at 22:13, Juan Sequeda wrote:
>
> This is a non lean RDF graph and per the RDF semantics, they are
> equivalent.
>
> Gotta love the RDF semantics.
>
> So, even though they are equivalent per RDF semantics, we still maintain
> the cardinality. But if we query in SPARQL, we get two different things.
> Therefore, there is a mismatch between the semantics of SPARQL and RDF.
> Interesting, eh?
>
> Juan Sequeda
> www.juansequeda.com
>
> On Apr 24, 2012, at 9:53 PM, David McNeil <dmcneil@revelytix.com> wrote:
>
> On Tue, Apr 24, 2012 at 1:44 PM, Richard Cyganiak <richard@cyganiak.de
> > wrote:
>   _:1 <IOU#BORROWER> "Alice".
>   _:1 <IOU#AMOUNT> 10.
>   _:2 <IOU#BORROWER> "Alice".
>   _:2 <IOU#AMOUNT> 10.
>
> Maybe I don't understand blank nodes properly. I thought the graph above
> was asserting the existence of two unique resources (since there are two
> blank node IDs).
>
> Thanks.
> -David
>
>
>