Fig. 2
From: Comparison between behavioral and structural explanation in learning by model-building
Behavior of the bathtub model. This is one of the possible behaviors of the bathtub model in which the amount of water gradually decreases to become steady (i.e., input and output are in equilibrium). Behavior is represented as a sequence of qualitative states (each of which is a set of qualitative values of parameters of the system). When sufficient information is not provided for determining the unique behavior, all of the possible behaviors are enumerated because of ambiguity. In this example, depending on initial condition, the amount of water could gradually increase to become steady, or become almost zero