- From: Alexandre Bertails <bertails@w3.org>
- Date: Wed, 19 Jan 2011 17:07:46 -0500
- To: Lee Feigenbaum <lee@thefigtrees.net>
- Cc: David McNeil <dmcneil@revelytix.com>, Eric Prud'hommeaux <eric@w3.org>, RDB2RDF WG <public-rdb2rdf-wg@w3.org>
Hi Lee,
On Wed, 2011-01-19 at 13:40 -0500, Lee Feigenbaum wrote:
> On 1/19/2011 11:43 AM, David McNeil wrote:
> > On Wed, Jan 19, 2011 at 10:29 AM, Eric Prud'hommeaux <eric@w3.org
> > <mailto:eric@w3.org>> wrote:
> >
> > At the end of 2006, Fred Zemke interceded to keep the
> > SPARQL semantics from having ambiguous cardinality, which cost months
> > but gave us invaluable definition in the semantics.
> >
> >
> > Eric - Can you elaborate on this and/or provide a link to what you are
> > referring to? In particular I am trying to understand the cardinality
> > semantics defined by SPARQL.
>
> The SPARQL algebra operates over multisets of solutions, and the algebra
> operations all define how they affect the cardinality of the solutions.
> To take a very simple example:
>
> {
> ?s :p :o
> } UNION {
> ?s :p :o
> }
>
> against the data:
>
> :s :p :o .
>
> Results in this solution (multi)set:
>
> ?s
> --
> :s
> :s
>
> In the absence of the DISTINCT or REDUCED keywords, any compliant SPARQL
> implementation must give you 2 copies of the ?s=:s solution in response
> to this query.
Does it mean that SPARQL cannot be implemented using Datalog? If I
understand well, there will be no way to be correct against the
semantics as Datalog relies on sets.
Alexandre.
>
> Lee
>
> >
> > Thank you.
> > -David McNeil
>
>
Received on Wednesday, 19 January 2011 22:07:44 UTC