Eecient Mining of Emerging Patterns: Discovering Trends and Diierences

We introduce a new kind of patterns, called emerging patterns (EPs), for knowledge discovery from databases. EPs are deened as itemsets whose supports increase signiic-antly from one dataset to another. EPs can capture emerging trends in timestamped databases, or useful contrasts between data classes. EPs have been proven useful: we have used them to build very powerful classiiers, which are more accurate than C4.5 and CBA, for many datasets. We believe that EPs with low to medium support, such as 1%{ 20%, can give useful new insights and guidance to experts, in even \well understood" applications. The eecient mining of EPs is a challenging problem, since (i) the Apriori property no longer holds for EPs, and (ii) there are usually too many candidates for high dimensional databases or for small support thresholds such as 0.5%. Naive algorithms are too costly. To solve this problem, (a) we promote the description of large collections of itemsets using their concise borders (the pair of sets of the minimal and of the maximal itemsets in the collections). (b) We design EP mining algorithms which manipulate only borders of collections (using our multi-border-diierential algorithm), and which represent discovered EPs using borders. All EPs satisfying a constraint can be eeciently discovered by our border-based algorithms, which take the borders, derived by Max-Miner, of large itemsets as inputs. In our experiments on large and high dimensional datasets including the US census and Mushroom datasets, many EPs, including some with large cardinality, are found quickly. We also give other algorithms for discovering general or special types of EPs.