External interfaces to component classes are defined primarily through the use of connectors. Assume that we have a definition of a Tank model in a model library. The model has an external interface in terms of the connectors inlet and outlet, as well as a formal class parameter TankStream which is a connector class with its default class value being the Stream connector class. (See ModelicaBook page 176)
We would like to extend the Tank model to include temperature dependent effects, analogous to how we extended a resistor to a temperature dependent resistor.
The definition of HeatTank is equivalent to the definition of HeatTankExpanded