part of part of BFO:0000050 part_of part_of uberon Everything is part of itself. Any part of any part of a thing is itself part of that thing. Two distinct things cannot be part of each other. 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 part and its whole http://www.obofoundry.org/ro/#OBO_REL:part_of is part of my brain is part of my body (continuant parthood, two material entities) my stomach cavity is part of my stomach (continuant parthood, immaterial entity is part of material entity) part_of this day is part of this year (occurrent parthood) has part has part overlaps axiom holds for all times