Re: example SQL mapping to direct graph

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