- From: Lee Feigenbaum <lee@thefigtrees.net>
- Date: Wed, 19 Jan 2011 13:40:29 -0500
- To: David McNeil <dmcneil@revelytix.com>
- CC: Eric Prud'hommeaux <eric@w3.org>, RDB2RDF WG <public-rdb2rdf-wg@w3.org>
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.
Lee
>
> Thank you.
> -David McNeil
Received on Wednesday, 19 January 2011 18:41:08 UTC