Study of complicated systems:
- A system is complex when it is composed of many parts that interconnect in intricate ways. (Joel Moses, "Complexity and Flexibility"). This definition has to do with the number and nature of the interconnections. Metric for intricateness is amount of information contained in the system
- A system presents dynamic complexity when cause and effect are subtle, over time. (Peter Senge, "The Fifth Discipline"). Egs: dramatically different effects in, the short-run and the long-run; dramatically different effects locally and in other parts of the system; obvious interventions produce non-obvious consequence
- A system is complex when it is composed of a group of related units (subsystems), for which the degree and nature of the relationships is imperfectly known. (Joseph Sussman, "The New Transportation Faculty"). The overall emergent behavior is difficult to predict, even when subsystem behavior is readily predictable. Small changes in inputs or parameters may produce large changes in behavior.