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Re: AW: Datalog DEXPTIME Complexity + Safe Execution of Recursive Axioms + English

From: Adrian Walker <adrianw@snet.net>
Date: Tue, 07 Oct 2003 10:26:21 -0400
Message-Id: <5.0.2.1.2.20031007100804.022a0090@pop.snet.net>
To: "Enrico Franconi" <franconi@inf.unibz.it>
Cc: <www-rdf-logic@w3.org>, <www-rdf-interest@w3.org>, voronkov@cs.man.ac.uk

Enrico --

It's possible that an important point is overlooked when many of us say 
things like "datalog can only compute things of polynomial complexity"

Andrei Voronkov kindly sent me a pointer to the excellent paper "Complexity 
and the Expressive Power of Logic Programming", that he wrote with Dantsin, 
Eiter and Gottlob.

In the paper, they point out that "complexity" can be "data complexity" or 
"program complexity".   The two are very different.

Data complexity  is the complexity of checking whether Din U P |= A for a 
fixed datalog
program P and variable input databases Din and ground atoms A.  It is 
"polynomial".

Program complexity is the complexity of checking whether Din U P |= A for 
variable datalog programs P and ground atoms A over a fixed input database 
Din.  It is complete in DEXPTIME.

Now it would seem that, if one is proposing a rule interpreter, then its 
inputs include variable datalog programs P.  So, the applicable complexity 
would appear to be "complete in DEXPTIME".

What do you think ?

                         Cheers --    Adrian



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Received on Tuesday, 7 October 2003 10:24:20 GMT

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