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Re: [Core] new definition of safeness

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Tue, 05 May 2009 13:04:07 +0200
Message-ID: <4A001D27.3030702@inf.unibz.it>
To: Dave Reynolds <der@hplb.hpl.hp.com>
CC: RIF <public-rif-wg@w3.org>

Dave Reynolds wrote:
> Jos de Bruijn wrote:
>> It turns out that the earlier definition of safeness I contrived is not
>> very extensible.  And as you may have noticed, it's not all that easy to
>> understand.  Also, it precluded the use of "output" variables of
>> external predicates to be used as inputs for other externals.
>> So, I came up with a new definition that addresses these issues:
>> http://www.w3.org/2005/rules/wiki/Core#Safeness
>> Please have a look.  The new definition uses a kind of normalization to
>> deal with disjunction and defines the notion of equivalence classes for
>> variables to deal with equality.
>> So, I needed some additional preliminary definitions, but the definition
>> of safeness itself is more straightforward.
> That looks good to me.
> Minor editorial - in the second bullet of the definition of the
> disjunction tree you don't need the primes over the n<sub>i</sub>, i.e.
> "has m child nodes n<sub>1</sub>, ..., n<sub>m</sub>" (or put primes
> over the references to them).

OK, thanks. I added the prime to the reference.

>> I will now work on the extension with strong safeness, which should not
>> be too hard.
> I found that difficult to follow but couldn't spot any problems.
> Minor editorial:
> o Suggest adding a second para something like:
> "The conformance clauses for RIF Core only require conformance over safe
> rule sets as defined above. However, some rule engines, such as some
> datalog engines, are only able to process rule sets which can be
> finitely grounded. For maximum interoperability with such systems it is
> recommended that RIF Core producers restrict themselves to strongly safe
> rule sets where possible."

OK, done.

> o In the first bullet the part "the terms in alpha in which ..." is
> confusing since alpha hasn't been defined. Perhaps that should be "the
> terms alpha in which ..."? Actually, I don't think alpha is referenced
> elsewhere either so it could be "the terms in which ...".

This should have been t instead of alpha. Now fixed.


> Dave

+43 1 58801 18470        debruijn@inf.unibz.it

Jos de Bruijn,        http://www.debruijn.net/
Many would be cowards if they had courage
  - Thomas Fuller

Received on Tuesday, 5 May 2009 11:04:59 UTC

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