An association rule mathematically describes the relationship items involved in various transactions. It does this by investigating the relationship between two itemsets in the form X ⇒  Y, where X ⊂, Y ⊂. In addition, X and Y are nonoverlapping itemsets; which means that  .

An association rule could be described in the following form:

{helmet,balls}⇒ {bike}

Here, {helmet,ball} is X and {ball} is Y.