  Modeling in software engineering includes constructing static, dynamic, and
behavioral representations. In describing system behavior, actions and states
are two of the most commonly used concepts. In this paper, we focus on the
notion of action. It generally held that the meaning of the concept of action
is not that easy to grasp. According to some researchers, many existing systems
do involve the notion of action, but in an obscure way. In Unified Modeling
Language (UML), an action is a single atomic step within an activity, i.e., it
is not further decomposed within the activity. Activity represents a behavior
that is composed of actions. This paper contributes to the establishment of a
broader interdisciplinary understanding of the notion of action in conceptual
modeling based on a model called the thinging machine (TM). The TM uses only
five primitive actions: create, process, release, transfer, and receive. The
goal of such a venture is to improve the process of developing conceptual
models by refining basic concepts such as action and event. To demonstrate how
TM modeling represents actions, UML activity and Business Process Model and
Notation (BPMN) diagrams are re-modeled in terms of the five TM actions. The
results reveal the viability of the TM s five actions in modeling and relate
them to other important notions such as activity, event, and behavior.
