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RE: [Core] updated safeness condition

From: Changhai Ke <cke@ilog.fr>
Date: Wed, 4 Feb 2009 15:20:48 +0100
Message-ID: <3E5E1A634BBD5C4A94C4D4A6DE0852E7021A1E55@parmbx02.ilog.biz>
To: "Jos de Bruijn" <debruijn@inf.unibz.it>, "RIF WG" <public-rif-wg@w3.org>

Hi Jos,

>From the view of PRD, the safeness means that each variable in the
conditions part (or the "body") must be initialized. So for each
variable, the engine must be able to find the expression that
initializes it.

Unlike the backward chaining rules, or the logic programming, which can
stack goals in a recursive way until they encounter facts, production
rules do not stack goals, they are data driven.

With this in mind, I try to read the definitions. It is indeed not
obvious to find to what extent this notion of "variable initialization"
is expressed in the new definition, while in the old one, the first
bullet reflects clearly this. If the old definition has a shortcoming,
can we adapt it?

If the new definition is indeed more precise, can you add a short text
saying that "intuitively the whole definition specifies each variable in
the body should be initialized".

Regards,

Changhai

> -----Original Message-----
> From: public-rif-wg-request@w3.org
[mailto:public-rif-wg-request@w3.org]
> On Behalf Of Jos de Bruijn
> Sent: Tuesday, February 03, 2009 7:05 PM
> To: RIF WG
> Subject: [Core] updated safeness condition
> 
> I updated the safeness condition to fix the technical problem I
noticed
> during the telephone conference and to improve the presentation.  I
hope
> it is now easier to follow.
> Please let me know if there are still problems in the presentation.
> 
> The problem with the previous version of the definition was that it
> allowed to assign "bound" to all variables, even those appearing only
in
> external terms.
> I now make a distinction between safe and strongly safe variables,
where
> the strongly safe variables are those that are made safe by
non-external
> atoms.  It is required that all variables that are not strongly safe
are
> assigned "unbound".
> 
> Please *read carefully* and criticize.
> And I remind you that it is not necessary to wait until the next
> telephone conference before starting to read the definition.
> 
> 
> Best, Jos
> 
> [1] http://www.w3.org/2005/rules/wiki/Core#Safeness
> --
> Jos de Bruijn            debruijn@inf.unibz.it
> +390471016224         http://www.debruijn.net/
> ----------------------------------------------
> No one who cannot rejoice in the discovery of
> his own mistakes deserves to be called a
> scholar.
>   - Donald Foster
Received on Wednesday, 4 February 2009 14:21:44 GMT

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