These and other types of models can overlap, with a given model involving a variety of abstract structures. The system is a set of interacting or interdependent entities, real or abstract, forming an integrated whole. The concept of an "integrated whole" can also be stated in terms of a system embodying a set of relationships that are differentiated from relationships of the set to other elements, and from relationships between an element of the set and elements not a part of the relational regime. A dynamical system modeled as a mathematical formalization has a fixed "rule" that describes the time dependence of a point's position in its ambient space. Small changes in the state of the system correspond to small changes in the numbers. The "evolution rule" of the dynamical system is a fixed rule that describes what future states follow from the current state. The rule is deterministic: for a given time interval only one future state follows from the current state.