Ontological dependency is a special poset because it is a binary relation, every thing is ontologically dependent on itself for its existence, two things that are mutually ontologically dependent must be the same thing and if a depends on b and b depends on c then a depends on c. The last of these properties - the transitive property of posets - was exploited by Helmut Hasse to give us the Hasse diagram - a diagram of incredible power, simplicity and if drawn well elegant as well. Because ontology charts have a root that all affordances (realisations/things) are ultimately dependent upon for their existence, they are graphical representation of semi-lattices.
