The quality and thus the validation of conceptual models are of high economic importance. However, only little empirical work has focused on their evaluation so far. This raises the question whether a holistic approach to determining the quality of conceptual models is available yet. In order to describe the current state of research and to expose the so far neglected research fields we develop a two dimensional framework. With the help of this framework we can identify a notable shortcoming on conceptual model evaluation. Contrary to models on theories a lot of empirical work has been performed. Therefore we apply the structuralist approach from philosophy of science in order to develop an inner structure of conceptual models. Based on these findings we deduce the structural requirements that conceptual models shall meet. We explain the practical implications of our proposal and sketch an outlook to future scientific inquiries.