In a data processing system in which data to be processed is managed as processing-object data, and the processing-object data is processed in response to a designation, there are provided: data management means for managing the processing-object data together with processing-object attribute information indicative of an attribute thereof; processing designation means for designating a processing with respect to the processing-object data through a dialog performed with the user; processing execution means for executing a processing of the processing-object data in response to a designation performed by the processing designation means; and first processing result forecasting means for executing, when the dialog is performed, a forecast on a result of the processing by comparing processing-subject attribute information, which indicates an attribute of a processing to be executed by the processing execution means, with the processing-object attribute information, and for outputting to the user forecast notification information in accordance with the result of the processing obtained through the forecast.