tState StateSpace StateSubset associatedTo StateClass ("hierarchical state") FeatureState ActiveState PortState ResourceState ReactiveState SingleEvent PendingSate PendingState Synchronization MultipleEvent State PendingState Fig. 7.42 State concepts, symbols and acronyms for ports 7 Concepts and Notations for Process Control Systems Modelling Resource state and state space: A resource state for a port is a value of the service resource model that is associ- ated with a primitive service. The provider port in a service relation is in a resource state when no operation requests are pending. When a provider port is in a resource state, we say that the service relation is in a resource state as well. Resource states are the only stable states. A resource state represents a state that is known and can be specified. All other types of states (active states, interrupt states and pending states) are transient states. When the provider port is in a transient state, the resource state is unknown. The set of all resource states that are possible (accord- ing to the service resource model) is the state space of the service behaviour. Since the state space is defined by the service resource model alone, state defini- tions are independent of how states are represented in a state diagram. A particular state diagram notation technique is just one of numerous methods for representing a behaviour in a given state space. Often one makes a distinction between "finite state machines", FSM, and "extended finite state machines", EFSM. I must admit that it took me some time to realize that this is not two different kinds of state machines, just two different ways of representing the behaviour of a single state machine. A complete description of an FSM means that all individual resource states that exist in the state space are shown in a state diagram. Often, this is not possible or of interest, since the number of states can be hundreds or thousands. Describing a state machine as an EFSM diagram means that the state symbols shown in t