In the POLYMER ontology you can find some classes which do not have an associated formal definition, e.g. SYNTHETIC MATERIALS. The reason is that these classes do not contain any knowledge that is relevant for our application. However, they are used in standard textbooks [Dom88] for the classification of polymers. In order to design our ontology in a general way we have adopted them, too. Only the three classes THERMOPLASTICS, ELASTOMERS, and THERMOSETS play a crucial role. Their properties can be primarily described by the abstraction of the subsumed materials (instances and classes).
Furthermore, the POLYMER ontology contains a couple of instances which are the leaves in figure 7. However, we have only taken those materials as instance that have a fixed composition and properties. This is not the case for PC (Polycarbonat) that still shows an interval for the E--modulus quantity. In fact its actual properties depend on the manufacturer. Therefore, we have still defined this polymer as a class. The instances might be defined as a function of the manufacturer.