Oh? And why not?
For example, the Starwars-1 research problem had threat scenarios that went something like: " We have 300,000 incoming, what's real? what's not? we have 12 minutes to retrain our interceptors. Do we have time for a recursive Lisp algorithm?"
The answer to the last part of the question was "no". Recursive algorithms were too slow. The only way to meet the time constraints of the problem was to pre-identify all possible values of all possible variables and system states as a semantic mesh, and then to use incoming sensor data as reality constraints across this jungle gym of reasoning paths in order to ascertain the threat and take action in time.
The point is that the impact of all foreseeable reality constraints could be precomputed and the resulting declarative semantic web could be reasoned over in minimum time. Instead of a "no", the answer in this case was "yes".
On the other hand, the conclusion of the Star Wars I research was that, while researchers could beat a very complex and comprehensive set of threat scenarios, the military was unlikely to beat the potential enemy (in cold war days, it was usually the Russians) because the enemy could learn and adapt and do something unexpected. In short, they concluded that they could not foresee any and all possible threat scenarios. That is, their knowledge would remain incomplete.
So, to the limits of the knowledge (axioms, etc.) specified, the answer is "yes". I can precompute the implications of forward and backward chaining axioms. (The trade here is space vs time.)
In terms of reality, however, it seems that our "knowledge" is not "truth" but more a system of constraints. More often than not it is partial and incomplete, and likely to be in conflict or competition with other knowledge or values that we believe in.
Permit me to wax for a moment. I think the really interesting stuff of reasoning (e.g., questions where lives are on the line, questions of guilt or innocence, questions of ethics, questions about what is the best product design, or best course of action for a business, questions of public policy, or career choices) always involve more than logical consistency. They involve trade-offs and values. Often there is no "right" answer. Logic is just a tool.
On Sep 17, 2007, at 12:58 PM, Pat Hayes wrote:
Wouldn't the impact of all possible informational variables be (pre)computable at the time the backward/forward axiom was formulated?
No.
Pat
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