Re: Prototype SPARQL engine based on Datalog and relation of SPARQL to the Rules Layer

Reading this, I noted one direct request of the working group, which I
respond to inline.

On Sun, Dec 03, 2006 at 03:21:03AM +0100, Axel Polleres wrote:
> 
> Dear members of the DAWG,
> 
> Over the last few months I did some investigation on the relations 
> between SPARQL and rules languages, more precisely between SPARQL and 
> Datalog.
> 
> The results are written down in the following technical report which I 
> hope contains some useful insights and which I also plan to send to the 
> SPARQL working group:
> 
> http://www.polleres.net/publications/GIA-TR-2006-11-28.pdf
> 
> You find the following in there:
> 
> * I refine and extend the recent proposal to formalize the semantics of 
> SPARQL from Pérez et al., presenting three variants, namely c-joining, 
> s-joining and b-joining semantics.
> 
> * Based on these three semantic variants, I provide translations from a 
> large fragment of SPARQL queries to Datalog, which gives rise to 
> implementations of SPARQL on top of existing rules engines, a prototype 
> is available at http://con.fusion.at/dlvhex/download.php
> 
> * I'd like to suggest to the working group some straightforward 
> extensions of SPARQL such as adding the set difference operator MINUS, 
> and allowing nesting of ASK queries in FILTER expressions which come 
> basically for free in the approach.

This appears to be an implementation of UNSAID, which the WG has
decided to phrase as (for example):
  OPTIONAL { ?x dc:created ?created } .
  FILTER ( !bound(?created)) }
  http://www.w3.org/2001/sw/DataAccess/tests/#dawg-unsaid-002

Please examine the "unsaid" issue description
  http://www.w3.org/2001/sw/DataAccess/issues#unsaid
and advise us if you have novel information, or if you are satisfied
that the WG has discussed these points. You may close this thread by
responding to this messasge, prefixing the subject with [CLOSED].

> * Finally, I discuss an extension towards recursion by allowing 
> bNode-free-CONSTRUCT queries as part of the query dataset, which may be 
> viewed as a light-weight, recursive rule language on top of of RDF.
> 
> 
> My background is that in the RIF working group we discussed a while ago 
> how/whether to cover SPARQL queries in rule bodies there, which drew my 
> interest to the topic. I hope that sharing my insights with you this way 
> is also useful for the DAWG work.
> 
> Looking forward to comments/discussions!
> 
> best regards,
> Axel
> 
> 

-- 
-eric

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