Table 2.

Table 2 Operations Used in Scoring

Operator	Description	Usage	Scoring	Primary Use
AND	Probability both occur	A AND B	PA * PB	Weighting
OR	Probability either occurs	A OR B	PA + PB − PA * PB	Aggregating
NOT	Probability A does not occur	NOT A	1 − PA	Exclusion

Scores are treated as probabilities, P_A and P_B, of independent events, A and B. If finding a search term in the title gives a probability of 0.8 that the title is relevant, then finding a second occurrence yields an aggregate probability of 0.8 + 0.8 − 0.8² = 0.96.