Representing parthood relations in ORM has received little attention, despite its added-value of the semantics at the conceptual level We introduce a high-level taxonomy of types of meronymic and mereological relations, use it to construct a decision procedure to determine which type of part-whole role is applicable, and incrementally add mandatory and uniqueness constraints This enables the conceptual modeller to develop models that are closer to the real-world subject domain semantics, hence improve quality of the software.