Comments on "feedback control logic for forbidden-state problems of marked graphs: application to a real manufacturing system"

The AIP manufacturing testbed discussed by Ghaffari et al. (see ibid., vol. 48, p.18-29, 2003) was previously treated using automaton-based [as distinct from Petri net (PN)-based] supervisory control theory (SCT). Problems of this general type have been transcribed from the PN literature, sometimes greatly enlarged, converted into SCT format, and solved using integer-decision-diagram (IDD) techniques with only modest expenditure of time and memory. Thus it is substantially misleading to state, that "the AIP control problem would require huge processing time and memory if addressed with the Ramadge-Wonham [SCT] approach." In contrast to the restriction in Ghaffari et al. (2003) to "marked graphs", no prior structural restrictions other than finiteness of the state set (or boundedness in the case of PNs) were placed on the models of system components.