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Re: Append solution using pure production rules

From: Francois Bry <bry@ifi.lmu.de>
Date: Fri, 17 Mar 2006 09:04:17 +0100
Message-ID: <441A6D81.50408@ifi.lmu.de>
To: public-rif-wg@w3.org

Dear All,

As of whether or not production rules give rise to implement a recursive
computation process, the following should, I think, be considered.

Some brands of production rule languages, as they have been described in
the literature over the last 2 to 3 decades, significantly restrict the
re-firing of a rule that has already fired. In extreme cases, a rule can
only fire once. (Some other brands of production rule languages either
do not know such restriction or know such restrictions, but make it
possible to disallow them.)

If  the firing of a production rule at different cycles of the
computation is possible, then, in principal recursive computation can be
expressed. The proviso "in principle" is only necessary because of 
technicalities (such as primitives for list concatenation) that a given
production rule language might not offer.

It is worth stressing that proponents of production rule language have
in the past claimed that precluding recursion with production rules was
an advantage. (The oppositie viewpoint has often been expressed, too.)

I think, Hassan's remark should be understood in this historical context.

Thus, once again we are left with the observation that production rules
seems a well-defined computing paradigm, but in fact is not. It is a
nebula of languages each with different semantics. Indeed, there are no
general agreement on a common semantics for alll production rule
languages -- as opposed to declarative languages based on first-order
logic formulas and Horn clauses.

Regards,

François
Received on Friday, 17 March 2006 08:04:20 GMT

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