While many data mining models concentrate on automation and efficiency, interactive data mining models focus on adaptive and effective communications between human users and computer systems. User requirements and preferences play the most important roles in human-machine interactions, and guide the selection of target knowledge representations, operations, and measurements. Practically, user requirements and preferences also decide strategies of abnormal situation handling, and explanations of mined patterns. In this article, we discuss these fundamental issues based on a user-centered three-layer framework of interactive data mining.