Extending Association Rules
Association rule methods can be extended in several different ways. The most obvious extension is adding additional items on the left-hand side. Another extension is to have entirely different sets of items on the left-hand side and the right-hand side. And, perhaps the most interesting extension is the creation of sequential association rules, which look for patterns of items purchased in a particular order.
Multi-Way Associations
Association rules can have more than two items on the left-hand side. The mechanism is to continue adding in joins for every possible item, similar to the method for going from one item on the left-hand side to two items. As the number of items grows, the size of the intermediate results storing the candidate rules can get unmanageably large and take a long, long time to generate. The way to handle this is by adding restrictions so fewer candidate rules are considered.