Rules for Knowledge Representation
One way to represent knowledge is by using rules that express what must happen or what does happen when certain conditions are met.
Rules are usually expressed in the form of IF . . . THEN . . . statements, such as: IF A THEN B This can be considered to have a similar logical meaning as the following: A→B
A is called the antecedent and B is the consequent in this statement.
In expressing rules, the consequent usually takes the form of an action or a conclusion.
In other words, the purpose of a rule is usually to tell a system (such as an expert system) what to do in certain circumstances, or what conclusions to draw from a set of inputs about the current situation.
In general, a rule can have more than one antecedent, usually combined either by AND or by OR (logically the same as the operators ∧ and ∨).
Similarly, a rule may have more than one consequent, which usually suggests that there are multiple actions to be taken.
In general, the antecedent of a rule compares an object with a possible value, using an operator.
For example, suitable antecedents in a rule might be
IF x > 3
IF name is “Bob”
IF weather is cold
Here, the objects being considered are x, name, and weather; the operators are “>” and “is”, and the values are 3, “Bob,” and cold.
Note that an object is not necessarily an object in the real-world sense—the weather is not a real world object, but rather a state or condition of the world.
An object in this sense is simply a variable that represents some physical object or state in the real world.
An example of a rule might be
IF name is “Bob”
AND weather is cold
THEN tell Bob ‘Wear a coat’
This is an example of a recommendation rule, which takes a set of inputsand gives advice as a result.
The conclusion of the rule is actually an action, and the action takes the form of a recommendation to Bob that he should wear a coat.
In some cases, the rules provide more definite actions such as “move left” or “close door,” in which case the rules are being used to represent directives.
Rules can also be used to represent relations such as:
IF temperature is below 0
THEN weather is cold
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