The necessity of taking into account high-level information has recently been reported by the information fusion community. We previously presented an approach for high-level symbolic fusion that relies on the use of the conceptual graphs model. Domain knowledge is a major point of the fusion process. The use of conceptual graphs for knowledge representation eases the process of expressing domain knowledge and fusion heuristics. We use conceptual graphs in order to model a situation of interest. Information items extracted from different sources are fused, using the model of situation in order to orient the fusion by delivering a context. This article details a step that was introduced prior to fusion, that aims at testing the compatibility of observations. It explains the way the domain knowledge is introduced inside the compatibility test, similarly as it was previously introduced in the fusion process. The proposed approach is illustrated within the context of a decision support system for geopolitical crisis management.