The influence of Part-Whole relationship (partof) on ontology languages is weak because the special semantics of partof is missed in both representations and interpretations. In this paper, we first exemplify the complexity and limitation of using partof for representing wholes. We then investigate the special semantics of partof by analyzing the properties of parts and wholes. The conclusion is that a part should be regarded as something internal to certain whole and a whole is a structured thing which is comprised of some internal things. The special semantics are achieved by introducing some new constructs which are whole structure, part type, role type, Ontology, defined-in relation and play relation. Because the whole structure possesses inherent modularity and local semantics, the representation is very natural and simple. We show the generality and applicability of the presented approach in terms of the problems pointed out in the paper.