1. A method for generating a context hierarchy, the method comprising: (a) vertically projecting a frequent itemset tree for continuously generated transactions into a plurality of boundaries and generating new first transactions and new frequent itemset trees of each boundary by assigning an index to basic itemsets of each boundary; (b) detecting ones of the frequent itemsets of the new frequent itemset trees as a single context when the difference in support is a predetermined value or less and generating a context trees of a hierarchical structure based on the detected contexts; (c) generating a lowermost layer having a context hierarchy by assigning a new name to only contexts selected in the context trees; (d) generating new second transactions for a subsequent layer as a new name assigned in a previous step and generating new context trees; and (e) determining that there are no selectable contexts in the contexts of the new context trees and if not, ending the generation of the context hierarchy and if so, repeatedly performing the process from step (d) after assigning the new name to each context by selecting appropriate contexts and generating the subsequent layer having the context hierarchy.