An analysis of the control hierarchy modelling of the CMS detector control system

The high level Detector Control System (DCS) of the CMS experiment is modelled using Finite State Machines (FSM), which cover the control application behaviours of all the sub-detectors and support services. The Joint Controls Project (JCOP) at CERN has chosen the SMI++ framework for this purpose. Based on this framework, the functionality and behaviour of the equipments and subsystems of the experiment is represented as a collection of objects in a hierarchical structure where commands flow down and states flow upwards. The FSM tree of the whole CMS experiment consists of tens of thousands of nodes. Due to the enormous size and complexity of the system, a high level of homogeneity and consistency is desired. The analysis of the current FSM hierarchy of the CMS experiment and the design of a mechanism for the optimization of the FSM logic and structure is presented. The CMS FSM system is discussed in view of most recent research on modelling and analysis of such systems. A methodology for describing and analyzing complex FSM systems is presented.