Frequent Itemset Mining (FIM) is one of the most important data mining tasks. The characteristics of the mined datasets have a significant effect on the performance of FIM algorithms. Sparseness of datasets is one of the attributes that characterize the essential characteristics of datasets. Different types of FIM algorithms are very different in the scalability of dataset sparseness. Aiming at the measurement of sparseness of datasets and influence of sparsity on the performance of different types of FIM algorithms, the existing measurement methods were reviewed and discussed, then two methods were proposed to quantify the sparseness of the datasets:the measurement based on transaction difference and the measurement based on FP-Tree method, both of which considered the influence of the minimum support degree on the sparseness of the datasets in the background of the FIM task, and reflected the difference between the frequent itemsets of the transaction. The scalability of different types of FIM algorithms for sparseness of datasets was studied experimentally. The experimental results show that the sparseness of datasets is inversely proportional to the minimum support, and the FIM algorithm based on vertical format has the best scalability in three kinds of typical FIM algorithms.

In order to deal with coordinated attacks in Peer to Peer (P2P) systems, a blind intrusion detection algorithm was given based on digital whiff. Through "digital whiff" technology, the algorithm can find blood intrusion behaviors. Then it protects the systems from intrusion by cutting the multi-access and so on. Performance analysis and simulation results show the algorithm has better veracity and lower cost.