[PRD] Safeness in PRD (Was: Re: AW: AW: RIF Internal reviews)

Gary,

(I move this to the general mailing list)

gary.hallmark@gmail.com wrote on 26/05/2009 17:19:19:
> 
> I think safety must be linked to pattern matching. In fact, according
> to the Core document, safety is in Core precisely because it is
> required for a forward chaining implementation such as PRD. The little
> reference I added to safety is, I think, the only reference to safety
> in all of PRD.

In the current version of PRD, safeness is required for conformance, as in 
Core. That is the only place where it is explicitly mentioned, and, I 
agree with you, it is not enough.

> But you removed that. This cannot be correct.

I removed your reference, because safety is unrelated to the sentence 
where you added it.

The constraint that no rule can contain free variables and that all the 
variables that are free in a rule's action block must be bound in the 
condition or a binding pattern (of the same rule) is a well-formedness 
condition for groups, since the operational semantics of rule sets depends 
on it.

I thought that it was there, in some form (although not as a reference to 
safeness), but it is not.

So, that is the place where it must be added. For now, I just added a 
safeness condition in the definition of well-formed groups, that refers to 
the definition of safeness in Core. But that is not enough: I realized 
that we must extend the definition of safeness for PRD, because of the 
negation...

> We must
> reference somewhere the safety definition, and state that safety is
> required for PRD (possibly add to a well-formedness section?)
> 
> Also, priority and recency are total orders, because they are integers.

You are right, of course. I do not know what I had in mind when I thought 
that the priority or recency orders were partial...

Cheers,

Christian


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