More on Production Systems

Why Do People Build Production Systems?

• Because they can sometimes solve problems for us automatically. For example, a production system might partially simulate an expert in a field such as medicine, law, or chemistry.
• Because they may be a way to model and better understand human cognition. For example, a production system might tell us how a person attempts to solve an Eights puzzle or produces a sentence.

Some More Details

• The individual "facts" which make up Working Memory and the parts of both sides of rules are called clauses.
• In our production system language, all clauses will be surrounded by parentheses.
• There is normally no ordering to the clauses in Working Memory. Working Memory really means: CLAUSE1 and CLAUSE2 and CLAUSE3 ...
• Unlike English sentences, clauses begin with the symbols for the relations that tie the parts of the fact together or with NOT if the fact is negative: (GIVE MARY CD24 JOHN), (DIED ABRAHAM_LINCOLN 1865), (NOT (COMPREHEND CHARLIE_BROWN (SPEECH-OF TEACHER35)))
• Within clauses the order of the things does matter: (GIVE MARY CD24 JOHN) is not the same as (GIVE MARY JOHN CD24)
• Inside clauses, a single "thing" can either be a symbol, like JOHN or CLAIM or GREEN or XQTHRM003 or a group of symbols surrounded by parentheses, like (PERSON (AGE 35) (SSS# 335907765)) or (WORD (A MER I CA)).
• Pattern matching works roughly like this:
  • A clause matches another clause only if all of the corresponding parts match. The order of the parts matters.
  • A variable (something like ?X or ?CENTER or ?YGNNEE) matches any single thing, for example, JOHN or (WORD (A MER I CA)), but not JOHN MARY. But once a variable matches something, it is "bound" to that thing until you finish with the rule. So if you run into the variable a second or third time in the rule (on either the left-hand or right-hand side), it only matches thing it matched the first time (its "binding"). When you start over again with a rule or try to match a new rule, the bindings go away and variables again match anything.
  • A symbol other than a variable matches a variable (unless the variable is already bound to something else) or exactly the same symbol. So JOHN matches JOHN and ?Z, and ABOVE matches ABOVE and ?Q but not OVER.
  • An expression with parentheses around it inside a clause matches a variable (unless the variable is already bound to something else) or another expression if all of the corresponding parts match. So (PERSON (AGE 35) (SSS# 335907765)) matches (PERSON (AGE 35) (SSS# 335907765)) or ?WHOEVER or (PERSON (AGE ?AGE) (SSS# ?SSS#)) or (PERSON ?S ?T), but not (PERSON ?J).

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Last updated: 16 November 1995
URL: http://www.indiana.edu/~gasser/rules3.html
Comments: gasser@salsa.indiana.edu
Copyright 1995, The Trustees of Indiana University