1. A method for modeling connections of a system having a plurality of components and connections, the connections being located to connect the components to each other, the method comprising: modeling components of the system; modeling signal levels for nodes of the system as a variable, wherein the nodes of the system are representative of the connections; and modeling each potential component terminal connection of the connections which could potentially influence the signal level on each of the nodes as a qualitative variable, wherein each node of the system is modeled with n+1 variables, and the components which are modeled include devices which explicitly determine whether drive outputs can be directly modeled.