For use in recording has_part with a cardinality constraint, because OWL does not permit cardinality constraints to be used in combination with transitive object properties. In situations where you would want to say something like 'has part exactly 5 digit, you would instead use has_component exactly 5 digit.
w 'has component' p if w 'has part' p and w is such that it can be directly disassembled into into n parts p, p2, p3, ..., pn, where these parts are of similar type.
The definition of 'has component' is still under discussion. The challenge is in providing a definition that does not imply transitivity.