Virtual finite-state machine

A finite state machine defined in a virtual environment, called Virtual finite state machine ( eng. Virtual Finite State Machine, VFSM ). VFSM specification is a technique used to describe the behavior of logic systems by means of input - output characteristics and control actions.

VFSM introduces a logic execution model and allows the realization of an executable specification. This technology is mainly used in complex machine control systems, instrumentation and telecommunications applications.

Control properties

A variable in the environment of a VFSM can have one or more values ​​that are relevant for the control - then it is an input variable. These values ​​are referred to as control properties of this variable. The control properties are not necessarily specific data values, but mostly certain states of the variable. For example, a digital variable according to the possible Boolean data values, the control property to TRUE or FALSE, but also have UNKNOWN. A numeric variable analog control has properties such as LOW, GOOD, HIGH or UNKNOWN corresponding to the predetermined range of values ​​. A timer is OVERFLOW have as the most important control feature, others might be or IS RUNNING.

Actions

A variable in the environment of a VFSM can be activated by actions - then it is an output variable. For example, knows a digital variable two actions: True and False. A numerical analogue variable knows an action: Insert. A timer that is both an input and output variable that can be activated by actions such as start, stop or reset.

Virtual Environment

The Virtual Environment characterizes an environment in which the VFSM acts and which is defined by three sets of names:

  • Input names, represented by the control features of any variable
  • Output name, represented by all the possible actions that can be accepted by the variables
  • State name, defined for the states of the FSM

The input names are used to build virtual conditions and to control state transitions and input actions. The virtual conditions are created with the help of Positive Logic algebra. The output names are used to trigger actions ( Eingangsakationen, output actions, input actions and transition actions).

Positive Logic Algebra

To build virtual conditions, the Boolean operators AND and OR are used. The NOT operator is not allowed because the input name can not be negated, even if they obviously describe Boolean variables. They simply exist or do not exist.

VFSM execution model

A subset of all the defined input name, which can exist only in a particular situation is known as virtual input ( eng. Virtual Input, VI). For example, the temperature may either too low or too high to be good. Although three input names are defined, only one of you exist in a given situation. This name belongs to the VI.

A subset of all defined output name that can only exist in a particular situation is referred to as Virtual Output ( eng. virtual output, VO ). VO consists of the current actions of the VFSM.

The specification of the behavior, which contains all the details of a state of the VFSM is described by a state table.

The VFSM execution is determined by VI and the current status. Taking into account the specification of the behavior of the current state VO is set.

The graph shows a possible implementation of VFSM version. Based on the implementation, there is a typical behavior of the system.

State table

A condition table defines all the details of a state of a VFSM. It consists of three columns: the first column state names are used, built in the second column of the virtual conditions of entry names with the help of Positive Logic Algebra and in the third edition appear the name.

The table must be read as follows: the first two lines define the input and output operations of the current state. The following lines represent the input actions. The rows in which the next state is defined, describing the state transitions and the transition action. All fields are optional. A combinatorial VFSM is built, using only the lines are used for input actions. Transition actions may be replaced by corresponding use of the other actions.

Tools

  • State Works - An implementation of the concept VFSM (English)

Credentials

  • Ferdinand Wagner: Modeling Software with Finite State Machines: A Practical Approach, Auerbach Publications, 2006, ISBN 0-8493-8086-3
  • The Virtual Finite State Machine Design and Implementation Paradigm, Bell Labs Technical Journal, 1997 ( English)
  • Automata Theory
Finite-state machine
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