The work presented in the context of this paper is to develop a decision support system for security analysis called Adast. Adast is based on Case-Based Reasoning (CBR) and ontologies to help capitalize and exploit the knowledge on railroad accidents from our field of application. The advantage of this approach, based primarily on case-based reasoning and ontologies, lies not only on the capitalization of knowledge from experience feedback, but also on benefit in order to provide assistance to domain experts in their crucial task of analyzing and Improving security. In this paper, we will present the first realized works of Adast