The Parameterized Complexity of Enumerating Frequent Itemsets ⋆

Abstract. A core problem in data mining is enumerating frequentlyoccurring itemsets in a given set of transactions. The search and enumeration versions of this problem have recently been proven NP-and #P-hard, respectively (Gunopulos et al, 2003) and known algorithms all have running times whose exponential terms are functions of either the size of the largest transaction in the input and/or the largest itemset in the output. In this paper, we analyze the complexity of the size-k frequent itemset enumeration problem relative to a variety of parameterizations. Many of our hardness results are proved using a recent extension of parameterized complexity to solution-counting problems (McCartin, 2002). These results include hardness for versions of this problem based on restricted transaction-set structure. We also derive a collection of fixed-parameter algorithms using off-the-shelf parameterized algorithm design techniques, several of which suggest new algorithmic directions for the frequent itemset enumeration problem.