Our research is investigating the relationship between design problem formulation and creative outcome. Towards that goal we have conducted experiments with designers engaged in problem formulation. In order to analyze such empirical data, a formal representation is needed. One popular model is the Function-Behavior-Structure (FBS) model and its several variants. Our problem map (P-map) model shares many common features with FBS but also many differences. A symmetric hierarchical representation is introduced not only in each of the three domains (F, B, S) but in additional domains (requirements and issues). Generic inter and intra-domain relationships between these entities are also identified in addition to optional attributes of the entities, leading to a more expressive and flexible model that is domain independent and well suited for representing problem formulations of designers with different expertise levels and creativity. The model has been used for coding protocol data in a formal predicate logic language (Answer Set Programming).