The nine basic bond graph components are implemented as specializations of one superclass BGComponent and are hierarchically ordered based on the physical nature of their primitive behavior (see Fig. 2). In the bond graph model these components are shown in black, see Fig. 1.
The hierarchy of the block diagram formalism is shown in Fig. 3. In the bond graph model, these components are shown in gray (or blue on a color screen), see Fig. 1. The class Int requires a different implementation because it is the only block diagram element with a state. The class Clock is treated different from the other block diagram elements because it is the root for propagating known model variable values.
Three types of connections are possible. Connections between the bond graph components are made by power bonds, shown as black harpoons, e.g., between v and m1 in Fig. 1. Individual effort and flow variable values can be tapped from power bonds by active bonds. These are shown as black arrows, e.g., the input to the Int component angle in Fig. 1. Connections that originate from block diagram components do not carry energy and are called signals. These are shown as gray (blue) arrows. Because of their common characteristic, at times active bonds are referred to as signals as well. In Fig. 1 the connections between the Int, Cos, and Sum (`+') components are signals. A number of built-in constraints prevent undefined connections such as from a bond graph component to a block diagram component.
