reasoning with rules  production systems (생성시스템)  
rule-based systems (most of the expert systems) are sometimes called “production systems using rules” or simply “production systems”.
production system consists of fact base, rule base and inference engine (reasoning module).
fact base (short-term memory or working memory): a set of facts rule base (long term memory): a set of rules:
form if <condition> then <results> ….or actions in <results>.
inference engine: applies an applicable rule to facts (rule triggering,
or rule firing) to find new fact or to perform an action.
-needs conflict resolution (충돌해소)-select one rule to apply (depth first, best first, etc.) ex.dfs, bfs, b&b, bestfs,a*
facts  rules  ie  inferred facts  actions  53    forward chaining  54  
ex.did wilma love barney?
state consists of:  
man(fred), man(barney),woman(wilma), spouse(fred,wilma), friend(fred, barney)
rules are:  if man(x) or woman(x) then person(x)  
if person(x) and spouse(y, x) and friend(y, z) then ~love(x, z),
…  steps  
woman(wilma) applied to first rule ⇒ person(wilma) person(wilma) and spouse(fred,wilma) and friend(fred, barney) applied to second rule ⇒ ~love(wilma, barney)
  backward chaining  55  example  ~love(wilma, p)  ↑ z/p  person(wilma), spouse(y,wilma), friend(y, z)  ↑ fred/y  person(wilma), friend(fred, z)  ↑ barney/z  person(wilma)  ↑  woman(wilma)  ↑  none (the goal is proven)  
-interpretation using substitution list: ~love(wilma, barney)
  non-monotonic reasoning  (비단조추론)  
sometimes, old fact needs to be taken back.
wet(grass) and if rains(x) then wet(x), we concluded rains(grass).
but later, find sprinkler-on(grass), then we need to retract the fact
rains(grass).
in this case, production system needs to perform non-monotonic reasoning.
to perform non-monotonic reasoning, production system sometimes maintains a tms(truth maintenance systems) to maintain truth values for all clauses in working memory, instead of retract the facts.
ex) rains(grass)[0] where [1] true, [0] uncertain, [-1] false
56    handling uncertainties  57  
in reality, almost everything is uncertain.

especially in natural and social systems. ex   (이하 생략)