Modeling is the shared activity for both modeling and simulation, and knowledge representation. At the same time, the objectives of these two domains are not the same and both seem necessary when dealing with modeling highly structured and complex systems. To face the complexity of the systems we are trying to model and to simulate nowadays, the challenge addressed in this paper is to mix both approaches in a common framework. We first describe separately the recent advances made in the modeling and simulation community as well as in the knowledge representation community. We show that, despite the same goal to describe a reality, or at least a part of it, it results in very different, although related concepts. This difference is due to the focus taken by these communities. The first community is centered on dynamics, and the second one on static descriptions. From the analysis of the differences and similarities, we propose an architecture which is being tested in a modeling and simulation platform: Mimosa. The outcome is a formal way to pave the path from conceptual to running models which is sketched in this paper. The achievements and the perspectives are discussed in the conclusion.