- From: Richard Cyganiak <richard@cyganiak.de>
- Date: Tue, 24 Apr 2012 23:55:58 +0100
- To: ashok.malhotra@oracle.com
- Cc: public-rdb2rdf-wg@w3.org
On 24 Apr 2012, at 23:49, ashok malhotra wrote: > OK. Let's ask an empirical question. If you start with the Relational table > [Alice, 10] > [Alice, 10] > > And apply DM to it, then, according to the spec, do you get > > _:1<IOU#BORROWER> "Alice". > _:1<IOU#AMOUNT> 10. > _:2<IOU#BORROWER> "Alice". > _:2<IOU#AMOUNT> 10. > > Just yes or no > > I'm not asking what you should get and I'm not getting into RDF lean and mean semantics. > I'm just asking what the spec says. Yes, you get those four triples. The spec as written uses the “non-lean” direct mapping. Richard > > All the best, Ashok > > On 4/24/2012 3:32 PM, Richard Cyganiak wrote: >> Hi Ashok, >> >> On 24 Apr 2012, at 22:07, ashok malhotra wrote: >>> It seems clear that DM should generate >>> >>> _:1<IOU#BORROWER> "Alice". >>> _:1<IOU#AMOUNT> 10. >>> _:2<IOU#BORROWER> "Alice". >>> _:2<IOU#AMOUNT> 10. >>> >>> If that's what the spec says, we are done. >> This assertion is based on what? >> >> To the best of my knowledge, the version above can only be implemented by either materializing the table, or by using Oracle-specific extensions, and it is incompatible with R2RML. (Someone smarter than me might still prove me wrong on this.) >> >> There is another semantically equivalent version that is much easier to implement with just vanilla SQL, and works with R2RML. >> >> What advantage do you get by choosing the more complex, SQL-incompatible, R2RML-incompatible version? >> >> As far as I can tell, the advantage is that you get a more “natural” RDF graph structure for an infrequent corner case (tables without PK). >> >> That advantage is not worth the cost and loss of compatibility. >> >> I'd be happy with allowing both versions, but given the facts above, I don't think I can agree to forbidding the simpler, SQL-standard-compatible, R2RML-compatible version. >> >> Best, >> Richard >> >> >> >>> There may well be a RDF semantics/SPARQL issue lurking here but that's another matter. >>> All the best, Ashok >>> >>> On 4/24/2012 1:13 PM, 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 >> >
Received on Tuesday, 24 April 2012 22:56:27 UTC