A direct process is one which has a causal agent and proceeds sequentially. Various aspects of a direct process are caused by interactions among the agents, which are dependent upon one another.
Cell division, which proceeds through three distinct phases, is an example of a direct scientific process. Each phase has a definite sequence through which it proceeds; events cannot occur until others are completed.
For more information, see:
Chi, M. T. H. (In press). Three types of conceptual change: Belief revision, mental model transformation, and categorical shift. In S. Vosniadou (Ed.), Handbook of research on conceptual change. Hillsdale, NJ: Erlbaum.