1. A data processing apparatus comprising: means for acquiring a first data file that stores information that serves as a key for integrating data and a definition file that stores a rule for integrating the data stored in a second data file based upon the key; means for integrating and presenting the data stored in the second data file based upon the key and the rule; means for allowing the user to input an instruction to add new data to the data thus integrated and presented by said presenting means, and an instruction to remove a part of the data; means for adding or removing information, which is stored in the first data file and which serves as a key, according to the instruction thus input; and means for notifying, when the first data file is modified by the means for adding or removing, the means for presenting accordingly; wherein when the means for presenting is notified by the means for notifying that the information that serves as a key is added to the first data file, the means for presenting reads and presents the data to be added based on the added key and the rule, and when the means for presenting is notified by the means for notifying that the information that serves as a key is deleted from the first data file, the means for presenting deletes the data corresponding to the deleted key from a screen.
15. A data processing apparatus according to claim 1 , further comprising: means for allowing the user to input an instruction to edit the data thus integrated and presented by said presenting means; and means for modifying the second data file that stores the data, according to the editing instruction.