To develop an Enterprise Data Model in Information Strategy Planning, it is essential that we first decide on the critical entities that need to be consistently managed in the enterprise. Identifying entities is a very crucial decision that has much influence on the subsequent phases in Information Engineering. Nevertheless, it is very subjective and usually depends on a decision makers experience and his/her own knowledge. In this paper, we propose a decision support system called CB*IMSS, which employs Case-Based Reasoning as the problem solution technique. By retrieving, analyzing and adapting some similar previous cases with a decision makers enterprise situations, this system can help them identify and decide the critical entities required for successful performance of the ISP.