RE: UNSAID vs MINUS

> -----Original Message-----
> From: public-rdf-dawg-request@w3.org [mailto:public-rdf-dawg-
> request@w3.org] On Behalf Of Simon Schenk
> Sent: 29 June 2009 10:36
> To: public-rdf-dawg@w3.org
> Subject: UNSAID vs MINUS
> 
> ACTION-32  http://www.w3.org/2009/sparql/track/actions/32

> 
> To revive the discussion on negation, I would like to point you to the
> overview of options for implementation at:
> http://www.w3.org/2009/sparql/wiki/Design:Negation

> 
> In particular, binary operators vs. FILTER expressions, and set based
> MINUS in SeRQL vs UNSAID are discussed. Note that MINUS in SeRQL !=
> MINUS in Mulgara (?), which has the same semantics as UNSAID.
> 
> Cheers,
> Simon

Good time to revive it.

(I reorganised the page end of Friday - didn't remove any text intentionally but I put the two options in separate sections.  I generally called it NOT EXISTS.)

To make progress on this, let's take it in two steps.

1/ Decide on UNSAID vs Set-MINUS, that is resolve to explore one design in depth

2/ Then take as a sub-issue of NOT EXISTS as to have a graph operator and/or a FILTER expression.

I propose we adopt the UNSAID/NOT EXISTS design.  The Set-MINUS seems to have no advantages because it is equivalent to an NOT EXISTS form, but requires each side to be a set, which would need to be worked through the rest of the language.

On the second part, I found it to be no more work as the graph operator is the introduction of  algebra-level filter.

	Andy