has part has part BFO:0000051 has_part has_part uberon Everything has itself as a part. Any part of any part of a thing is itself part of that thing. Two distinct things cannot have each other as a part. Occurrents are not subject to change and so parthood between occurrents holds for all the times that the part exists. Many continuants are subject to change, so parthood between continuants will only hold at certain times, but this is difficult to specify in OWL. See https://code.google.com/p/obo-relations/wiki/ROAndTime a core relation that holds between a whole and its part has part has_part my body has part my brain (continuant parthood, two material entities) my stomach has part my stomach cavity (continuant parthood, material entity has part immaterial entity) this year has part this day (occurrent parthood) overlaps has material contribution from axiom holds for all times