In this paper, we propose a process for small to medium scale multi-assignment problems. In addition to biddings, agents can give motivations to explain their choices in order to help decision makers break ties in a founded way. A group decision support system, based on Logical Information Systems, allows decision makers to easily face both biddings and motivations. Furthermore, it guaranties that all the agents are treated equally. A successful case study about a small course assignment problem at a technical university is reported.