In order to trace the changes of association rules over an online data stream efficiently, this paper proposes two different methods of generating all association rules directly over the changing set of currently frequent itemsets. While all of the currently frequent itemsets are monitored by the estDec method, all the association rules of every frequent itemset in the prefix tree of the estDec method are generated. For this purpose, a traversal stack is introduced to efficiently enumerate all association rules. These online methods can avoid the drawbacks of the conventional two-step approach. In an on-line environment, a user may be interested in finding those association rules whose antecedents or consequents are fixed to be a specific itemset. Since generating all the association rules may take too long to produce them timely, two additional methods, namely Assoc-X and Assoc-Y, are introduced. Finally, the proposed methods are compared by a series of experiments to identify their various characteristics.