Thoughts on Fuzzy Logic? 3

[Predictor]

Over the past few weeks, a lively debate has developed over on Usenet in comp.ai.fuzzy and one of the stats groups. While many different topics have been brought up, the participants seem to fall into two camps over the basic issue of whether fuzzy logic is legitimate or not.

I was wondering what peoples' thoughts were here? Do you use fuzzy logic?

 

[aalmeida]

Can you give a breife explanation of what is fuzzy logic please! I ask that because my first language is not English and I would like to make sure I understand your subject.
thanks AL Almeida
NT/DB Admin
"May all those that come behind us, find us faithfull"

 

[Predictor]

Fuzzy logic is a method for handling uncertainty. Rather than get into a deep explanation here, I will refer you to:

http://www.faqs.org/faqs/fuzzy-logic/part1/

If you are interested in learning more about applied fuzzy logic, try "The Fuzzy Systems Handbook" by Earl Cox. If you are interested more in the theory behind fuzzy logic, a good choice would be "Fuzzy Sets, Uncertainty and Information" by Klir and Folger.

 

[SkidsMcCoy]

It's an interesting question. And as a reformed philosopher, I have to ask what is meant by 'legitimate'.

It's a internally consistent system that can be used to model events in the real world. How could this be less legitimate than mathematics or binary logic?

 

[Predictor]

I think the usual criticisms of fuzzy logic revolve around an assumption that fuzzy logical truth values are equivalent to probability, which I think is a dubious assumption.

 

[aalmeida]

My point is Logic, Mathematic etc are Knowledge tools, and you pick and choose wich one to use based on your answer to these questions:
What(your requirments are? do you know about the data? the expected results are?)?
Where (is your data? on your data to apply the tool? the result goes to?)?
When(to apply the tool? the results will be available?)?
How (to apply the tool? how easy to understand the results?)? AL Almeida
NT/DB Admin
"May all those that come behind us, find us faithfull"

 

[jtm111]

Predictor said:

"I think the usual criticisms of fuzzy logic revolve around an assumption that fuzzy logical truth values are equivalent to probability, which I think is a dubious assumption."

I couldn't agree more. This is the heart of the matter.

The term "uncertainty" can be used in many ways. In statistics, uncertainty can be quantified as the standard deviation of the sampling distribution. If you want to reduce uncertainty, you collect more data.

However, in philosophy uncertainty can refer to conceptual uncertainty. For example, what is a "proposition?" 'The cat is on the mat' is a proposition. 'If you heat water to 100 degrees Celsius, it will boil' is a proposition.

But what about: 'If Eisenhower had failed in the Normandy invasion, Hitler would have won the war.'

Is THAT a proposition? It certainly has the FORM of one. Unfortunately, there is no clear rule. Counterfactual conditionals are a fuzzy case. We are UNCERTAIN whether it is a proposition or not. To the point: our uncertainty would not be mitigated by gathering more information. We already have all the information that is possible to have. Our uncertainty is conceptual.

Fuzzy logic, it seems to me, is useful for this kind of conceptual uncertainty. If we wanted to simulate an economic system, one might state a rule: if the economy goes into recession, then lower interest rates. Well, what if GDP does not actually stall, but instead grows sluggish and fails to respond to the usual economic stimuli. Are we in a recession? who knows. We want to say: "well the point is, it sure SEEMS like a recession, so let's call it a recession and solve the problem," at which point the rule kicks in.

Similarly in a control system: the engine is technically not overheating, but it is running very hot and the RPM's are getting fast (what is "fast"?)... therefore we invoke the rule to slow down the RPMs.

In short, statistical methods are useful when uncertainty is related to probability. i.e., when there IS a fact of the matter, but sampling error prevents us from seeing it clearly so we minimize our error (through maximum likelihood, sample size, etc).

In contrast, fuzzy logic is useful when uncertainty is conceptual, i.e. when there is NOT neccessarily a fact of the matter (except maybe by arbitrary conventions), so we must loosen our criteria so that our rule system mirrors our experience of the real world (e.g. well we are PROBABLY in a recession, or the engine is PROBABLY stressed, or a counterfactual conditional is SOMEWHAT like a proposition).

The philosophical points I made are based on Wittgenstein's analysis of ordinary language (Philosophical Investigations), which provides what I think is an outstanding basis for Fuzzy Logic.

 

[Guest_imported]

Do you know how to use fuzzy logic in database applications.I am using sql server 2000 and don't want to buy fuzzy query or tools similar to that.I have to write a script to obtain the best results by using fuzzy logic.But I don't know how to do it.I will be glad if anyone helps about this subject.

 

[Predictor]

I'm not a SQL expert, but I think most popular commercial implementations should provide enough math to allow construction of at least a simplistic fuzzy query. See the fuzzy logic FAQ (mentioned earlier in this thread) for a basic introduction.

 

[jnicho02]

Predictor, I read the posts above and FAQ with interest and from my calculations the degree of legitimateness of fuzzy logic is 0.63 ;-) Jeremy Nicholson, Director of

http://www.firstlightassociates.co.uk

a UK-based Java and Data Warehousing consultancy