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

On Wed, 2011-01-19 at 12:22 +0000, 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...

@Ivan sorry, I wasn't clear enough :-) Please translate my "I owe you
100" by this SQL query on the example above:
[[
mysql> SELECT SUM(Amount) FROM Debts WHERE Name = "Juan";
+-------------+
| SUM(Amount) |
+-------------+
|         100 |
+-------------+
]]

So you were totally correct when you said "two pairs of identical
triples with different subjects". And in my example, I owe Juan 2*50.

> Otherwise known as "RDF can't add, and (up until recently) neither can
> SPARQL". Which is a feature, not a bug, re decidability :)

@harry As I said above, nobody expects any triple with 100. Sorry for
the misunderstanding.

> 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.

You're right. The problem is that Datalog (and more generally any
predicate-based logic) is based on sets whereas the SQL user expects
multisets.

Alexandre.

> 
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> >
> > Ivan
> >
> >
> >
> >
> >
> >>
> >> Alexandre.
> >>
> >> [1] http://www.w3.org/TR/2010/WD-rdb-direct-mapping-20101118/#Rel
> >>
> >>
> >
> >
> > ----
> > Ivan Herman, W3C Semantic Web Activity Lead
> > Home: http://www.w3.org/People/Ivan/
> > mobile: +31-641044153
> > PGP Key: http://www.ivan-herman.net/pgpkey.html
> > FOAF: http://www.ivan-herman.net/foaf.rdf
> >
> >
> >
> >
> >
> >
> 
>

Received on Wednesday, 19 January 2011 13:59:46 UTC