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Re: safety and external predicates

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Tue, 12 Aug 2008 18:17:17 +0200
Message-ID: <48A1B78D.4000406@inf.unibz.it>
To: Axel Polleres <axel.polleres@deri.org>
CC: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>

It seems to me that if we want to have a notion of safeness in Core, we 
would want something like "domain-safeness" as described in [2] (page 281).
Essentially, it ensures that there is no recursion involving variables 
that do not occur in user-defined predicates in the body.  This ensures 
finiteness.

So, it would not be possible to write:
p(x) :- p(y), External(add(y,1,x))
p(1)
(which is the example Axel gave in the telephone conference today, and 
which leads to an infinite extension of P)

But it would be possible to write:
q(x) :- p(y), External(add(y,1,x))
p(1)
because there is no recursive dependency between q and any of the body 
predicates


Best, Jos

Axel Polleres wrote:
> 
> Two pointers here... the notion of strong safety in hex-programs [1,2] 
> and Topor's considerations on  safe database queries with arithmetics 
> [3] (cudos jos for the latter one)
> 
> 
> 1. R. Schindlauer. Answer-Set Programming for the Semantic Web. PhD 
> thesis, Vienna University of Technology, Dec. 2006.
> http://www.kr.tuwien.ac.at/staff/roman/papers/thesis.pdf
> 
> 2.  Thomas Eiter, Giovambattista Ianni, Roman Schindlauer, and Hans 
> Tompits. Effective Integration of Declarative Rules with External 
> Evaluations for Semantic Web Reasoning. In York Sure and John Domingue, 
> editors, Proceedings of the 3rd European Conference on Semantic Web 
> (ESWC 2006), Budva, Montenegro, number 4011 in Lecture Notes in Computer 
> Science (LNCS), pages 273-287. Springer, June 2006.
> http://www.springerlink.com/content/f0x23wx142141v44/
> 
> 3. R. Topor. Safe database queries with arithmetic relations (1991)
> Proc. 14th Australian Computer Science Conf 
> http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.48.4845
> 
> 

-- 
Jos de Bruijn            debruijn@inf.unibz.it
+390471016224         http://www.debruijn.net/
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Received on Tuesday, 12 August 2008 16:17:15 GMT

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