  A system s behavior is typically specified through models such as state
diagrams that describe how the system should behave. According to researchers,
it is not clear what a state actually represents regarding the system to be
modeled. Standards do not provide adequate definitions of or sufficient
guidance on the use of states. Studies show these inconsistencies can lead to
poor or incomplete specifications, which in turn could result in project delays
or increase the cost of the system design. This paper aims to establish a
precise definition of the notion of states and state machines, a goal motivated
by system modelers (e.g., requirement engineers) need to understand key
concepts and vocabulary such as states and state machine, which are major
behavioral modeling tools (e.g., in UML). State is the main notion of a state
machine in which events drive state changes. This raises questions about the
nature of these state-related notations. The semantics of these concepts is
based on a new modeling methodology called the thinging machine applied to a
number of examples of existing models. The thinging machine semantics is
founded on five elementary actions that divide the static model into
changes/states upon which events are defined.
