A conflict is a common phenomenon that results from the interaction between both individuals and groups of individuals. For the development of knowledge-based systems, one needs to multiply sources of expertise, so that one may be able to generate several types of conflicts from these sources. The classical approach which avoids dealing with conflicts is not suitable. Therefore, in order to capture the dynamics of the system properly, one needs to develop a model which contains a greater amount of information on all eventual conflicts. In this study, we have opted for the negotiation approach [5], known also as the co-operative approach. We apply the negotiation approach for the conflicts' resolution once the typology of the conflicts has been defined. In order to build a common ontology from different perspectives, we developed an Assistance Tool based on the negotiation method.