1. A simulation method for simulating operations of a plurality of processes sequentially executed in an object, said method comprising the steps of: holding rules for first interactions between an attribute of a part and another attribute of the part or an attribute of a child part of the part according to each part of the object, in a part data base; holding an execution order for the plurality of processes, a knowledge of relationships between a part used in each process and another part, and rules for second interactions between attributes of a medium and a part used in the operation in each process as a process model in a process model memory; and performing a simulation of the operations by determining statuses of attributes of parts and media after each of the processes, sequentially in the execution order held in the process model memory, using a model-based reasoning by referring to the first and second interactions, the knowledge of the relationship between the part used in each process and the another part and statuses of attributes of the parts and the media determined in a preceding process.