Re: Minutes of the 2010-01-18 telcon for the RDF2RDF WG

On Wed, 2011-01-19 at 14:03 +0100, Boris Villazón Terrazas wrote:
> On 19/01/2011 13:22, Harry Halpin wrote:
> >> On Jan 18, 2011, at 19:05 , Alexandre Bertails wrote:
> >> [snip]
> >>> Juan, in order to help you with your action, I would like you to
> >>> considerer the following:
> >>>
> >>> [[
> >>> CREATE TABLE Debts (
> >>> Name varchar(50),
> >>> Amount Integer
> >>> );
> >>> INSERT INTO Debts (Name, Amount) VALUES("juan", 50);
> >>> INSERT INTO Debts (Name, Amount) VALUES("juan", 50);
> >>> ]]
> >>>
> >>> Using this very simple RDB [1] example, can you go through all the
> >>> phases that lead to the RDF where I owe you 100?
> >>
> >> Alex, for my understanding: what I would expect to see in RDF are two
> >> pairs of identical triples with different subjects. How would a direct
> >> produce anything whereby I owe Juan 100? I will owe 50 twice, but the fact
> >> that this is a hundred is a step that the RDF per se cannot say...
> > Otherwise known as "RDF can't add, and (up until recently) neither can
> > SPARQL". Which is a feature, not a bug, re decidability :)
> >
> > However, I'm assuming Alex is asking with Datalog semantics, do you get
> > with those two insert statements *two* distinct pairs of triples
> > (multiset) or just one (set)?
> >
> > Multisets have repeated membership, while sets don't I think.
> Thanks Alex for pointing out this case.
> This case was included by Eric within the test cases
> http://www.w3.org/2001/sw/rdb2rdf/wiki/R2RML_Test_Cases_v1#DB5

You're right. I just made simpler and put it in the body of the email so
I was sure that people would look at it :-)

> So, as you said the question is what is the default mapping for this case?

Two triples with different bnodes as subjects.

> how we can face this case with R2RML? and what would be the expected result?

I have no idea.

The Denotational Semantics for the Direct Mapping (aka. the algebras and
the associated mapping function) *already* works on top of multisets
(and sets and lists), both in the data model for RDB and in the
higher-order functions we define/use to manipulate this data-structure.

Alexandre.

> 
> 
> Boris
> 
> 
> 
>

Received on Wednesday, 19 January 2011 14:07:01 UTC