1. A computer-implemented method of modeling a physical entity, comprising: programmatically representing a structure of a physical entity as an executable model, the model including a plurality of model elements that include at least one structural physical parameter and at least one model behavior, the structural physical parameter using at least one structural variable; receiving an input value for the at least one structural variable during a model execution; modifying the represented structure of the physical entity based on the received input value during model execution; and storing the represented structure of the physical entity in storage after the modifying.