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Re: safety and external predicates

From: Chris Welty <cawelty@gmail.com>
Date: Thu, 14 Aug 2008 10:23:54 -0400
Message-ID: <48A43FFA.3030802@gmail.com>
To: Axel Polleres <axel.polleres@deri.org>
CC: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>


I still am not convinced that safeness is anything more than an academic 
requirement for CORE.  I would like to hear from someone who is a) interested in 
CORE and b) has some idea what an implementation is and c) has some idea what 
users of CORE would need, to let us know if these requirements matter:

1) Decidability: is is important that RIF-Core have decidable reasoning? That 
is, any compliant RIF-Core reasoner (implementation) will be guaranteed to 
terminate on any rule-set?

2) If decidability is a requirement, is tractability?  That is, any 
implementation will terminate in worst-case polynomial time (or better?)

My general impression from talking to some potential RIF implementors is that 
they treat rule-bases like programs - if your programs don't work its your 
fault, go fix them.  However one important difference between rule/logic 
"programs" and procedural programs is the amount of control you have over the 
search strategy.  I think this is (a practical reason) why decidability is 
considered by some to be important for these languages and not for e.g. Java.

-Chris

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
> 
> 

-- 
Dr. Christopher A. Welty                    IBM Watson Research Center
+1.914.784.7055                             19 Skyline Dr.
cawelty@gmail.com                           Hawthorne, NY 10532
http://www.research.ibm.com/people/w/welty
Received on Thursday, 14 August 2008 14:24:44 GMT

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