Abstract: One embodiment of the invention provides a method for extending a schema of network parts types and part type attributes hard-coded by a CAD application. The network parts may be used to compose a CAD model. Users may extend the network part schema by adding an attribute or property for an existing network part, or define an entirely new part by associating the new network part with a set of part type attributes. At the same time, the CAD application may use either a hard-coded or dynamically assigned enumeration value to perform a variety of functions using both the hard-coded and user declared network part types and part properties. For example, functions such as searching a network part list or traversing the elements included in a CAD model may operate using the enumeration values, allowing the CAD application to perform these operations efficiently.