Will it take much time to take a decision based on the learned knowledge? If the purpose of the data mining process is to improve on planning time, this is a most relevant question. For a given set of r rules, what matters is how we find the rule to use. If the rules are sorted somehow, it may be possible to use indexing or search methods to find the right rule quickly. Otherwise, the complexity of taking the decision could be higher than if for instance all rules must be compared pairwise. For a decision tree, the complexity of decision making is usually some function of its width and height.