The invention concerns a method of establishing rules (14) for a specific device which is intended to be able to be used for generating decision support for decisions which determine the behavior of an entity (44) and/or for controlling the behavior of an entity (44). The device is, inter alia, arranged to present a decision support window which comprises at least one area (56) which represents a state (30), wherein this area (56) comprises names which identify different rules (14) which form part of the state (30). The method according to the invention comprises the steps that the device is run in a real or simulated version of said entity (44), that said decision support window is presented to a user, that the user makes decisions by inputting instructions, that the decisions which have been made by the user are analysed, and that the rules (14) for which the user has made decisions are determined or modified in accordance with the analysis which has been carried out.