# Re: [Core] new safeness condition

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Tue, 03 Feb 2009 17:36:28 +0100
Message-ID: <4988728C.1050603@inf.unibz.it>
To: Chris Welty <cawelty@gmail.com>
CC: RIF WG <public-rif-wg@w3.org>
```

Chris Welty wrote:
>
>
> From the new definition:
>
> "A rule implication φ :- ψ is safe if ?V1, ..., ?Vn are the variables
> appearing in ψ or φ, ?V1, ..., and ?Vn are safe in ψ, in the context of
> ψ, and there is a mapping θ from the variables to {b, u} such that "
>
> I'm having trouble understanding this context notion and to exemplify my

I agree it is a bit hard to understand; I will try to simplify it.

> misunderstanding I can't say whether "are safe in ψ, in the context of
> ψ," should be "are safe in φ, in the context of ψ," or "are safe in ψ,
> in the context of φ,".  Though I suspect the former, in other words the

No. The formulation is correct.

> conclusion needs to be safe "in the context of" the condition, which I
> think is there to ensure equality doesn't sneak into the conclusion?

No. The syntax definition of Core takes care of this.
The point is to ensure that if there is an equality statement ?x=?y in
the condition, ?x is only safe if ?y is safe in the condition formula
(the context here).

Best, Jos

>
> -Chris
>
> Jos de Bruijn wrote:
>> I found a problem with the definition when considering equality atoms.
>> I revised the definition; this should fix the problem.
>>
>> Best, Jos
>>
>> Jos de Bruijn wrote:
>>> I completed ACTION-687: Write a proposed new definition of the safeness
>>> restriction
>>>
>>> http://www.w3.org/2005/rules/wiki/Core#Safeness
>>>
>>>
>>> I suspect it can be a little more concisely.  When I find some time I
>>> will go over it again.
>>>
>>>
>>> I also invite anyone who is interested to go over the functions and
>>> predicates in DTB and check whether the binding patterns defined are
>>> appropriate.
>>>
>>> Best, Jos
>>
>

--
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 Tuesday, 3 February 2009 16:36:36 UTC

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