In a fault diagnosis or a process simulation arrangement, data is held on first interactions between attributes of a part and between attributes of a parent part and a child part according to object parts in a parts data base. Data on an order for executing processes and data on a process model describing each process operation as second interactions between attributes of a medium and a part used in the process operation are held in a process model memory. In the fault diagnosis, fault statuses of attributes of parts and media used in each process are determined as candidates for causes of effecting statuses of attributes corresponding to the fault of the following process in reverse order of the execution order held in the process model memory using model based reasoning by referring to the first and second interaction relationships and statuses of attributes of the parts and the media determined in the following process. The attributes of the parts and the media may be expressed as a tree structure. The simulation is performed by determining statuses of attributes of parts and media used in each process sequentially in the execution order held in the process model memory using model based reasoning by referring to the first and second interactions and statuses of the parts and media determined in a preceding process.