Definitions

Rules

The rules used throughout the software are in conjunctive form. That is, the rule consists of a set of conditions that make up the precondition and a single condition that is the postcondition. For example:

IF (age 10) AND (color = BLUE) THEN output = TRUE

The first part of the rule (before the THEN keyword) is called the precondition of the rule. The second part is called the postcondition. When searching for rules of a particular class, such as all loyal customers or fraudulent accounts, the postcondition is likely to be fixed to the class of interest.

Database and rule properties

The rule properties a,b,c and d are used on a number of screens where rules have been evaluated.

a

A score based on the number of records in the database for which the precondition of a rule holds.

b

A score based on the number of records in the database for which the postcondition of a rule holds (that is, the number of records that belong to the class of interest).

c

A score based on the number of times both the precondition and postcondition hold, that is when both a and b hold.

d

The number of records in the database.

 

Interest measures

 

Accuracy (also known as confidence)

defined as c / a

 

Coverage

defined as c / b

 

Applicability (also known as support)

defined as c / d