The role class “Unit” should be used for linked chained production plants. It is used for hierarchization. The definition of a “Unit” is given in IEC 62264-1:2013, 5.3.8: “Process cells and units are the lowest level of equipment for batch manufacturing processes. Units are usually only identified if there is flexibility in the routing of product within a process cell. The definitions for process cells and units are contained in the IEC 61512-1 standard. The major processing capability or family of products produced often identifies the process cell. Examples of process cell identifications are ‘Mixing Line #5’ and ‘Detergent Line 13’. Process cells and units have well-defined manufacturing capabilities and batch capacities.”