In the

Unified Modeling Language The Unified Modeling Language (UML) is a general-purpose, developmental modeling language in the field of software engineering that is intended to provide a standard way to visualize the design of a system. The creation of UML was originally m ...

, an action is a named element that is the fundamental unit of executable functionality. The execution of an action represents some

transformation Transformation may refer to: Science and mathematics In biology and medicine * Metamorphosis, the biological process of changing physical form after birth or hatching * Malignant transformation, the process of cells becoming cancerous * Trans ...

or processing in the modeled system. An action execution represents the run-time behavior of executing an action within a specific behavior execution. All action executions will be executions of specific kinds of actions because action is an

abstract class In programming languages, an abstract type is a type in a nominative type system that cannot be instantiated directly; a type that is not abstract – which ''can'' be instantiated – is called a ''concrete type''. Every instance of an abstra ...

. When the action executes, and what its actual inputs are, is determined by the concrete action and the behaviors in which it is used. An action is the specification of an

executable In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instruction (computer science), instructi ...

statement and is the fundamental unit of processing or behavior in an activity

node In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines, ...

that represents some transformation in the modeled system. An action forms an abstraction of a computational procedure which is an atomic execution and therefore completes without interruption. An action is considered to take zero time and cannot be interrupted. In contrast, an activity is a more complex collection of behavior that may run for a long duration. An activity may be interrupted by events, in which case it does not run to completion. An action is a result of a system

state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * ''The State'' (newspaper), a daily newspaper in Columbia, South Carolina, United States * ''Our S ...

change and is realized by sending a message to an

object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ...

or modifying a link or a

value Value or values may refer to: Ethics and social * Value (ethics) wherein said concept may be construed as treating actions themselves as abstract objects, associating value to them ** Values (Western philosophy) expands the notion of value beyo ...

of an

attribute Attribute may refer to: * Attribute (philosophy), an extrinsic property of an object * Attribute (research), a characteristic of an object * Grammatical modifier, in natural languages * Attribute (computing), a specification that defines a prope ...

. An action may receive inputs in the form of control flows and object flows (the latter via input pins) and passes the results of its processing or transformations to one or more outgoing control flows or object flows (the latter via output pins) and onto

downstream Downstream may refer to: * Downstream (bioprocess) * Downstream (manufacturing) * Downstream (networking) * Downstream (software development) * Downstream (petroleum industry) * Upstream and downstream (DNA), determining relative positions on DNA ...

nodes. Execution of the action cannot begin until all its prerequisites are satisfied. All incoming control flows have control tokens and all input pins have object tokens. An action refers to the suite of rules and policies associated with a

state machine A finite-state machine (FSM) or finite-state automaton (FSA, plural: ''automata''), finite automaton, or simply a state machine, is a mathematical model of computation. It is an abstract machine that can be in exactly one of a finite number o ...

, and is represented as an

method. Actions are contained within and are provided context by activities. An action behavior accompanies a transition event.

Action types

*''On Entry'': occurs when an activity is entered. *''Do'': occurs while an activity is occurring. These are the steps within the activity. *''On Exit'': occurs when you leave an activity. *''On Event'': occurs upon a specific

event Event may refer to: Gatherings of people * Ceremony, an event of ritual significance, performed on a special occasion * Convention (meeting), a gathering of individuals engaged in some common interest * Event management, the organization of eve ...

. Unified Modeling Language {{uml-stub