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<html>
<head>
<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Finite State Machines</title>
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<h1 xmlns:l="http://docbook.sourceforge.net/xmlns/l10n/1.0">Finite State Machines</h1>
<div class="section" title="Finite State Machines">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both">
<a name="FiniteStateMachines"></a>Finite State Machines</h2>
</div>
</div>
</div>
<div class="section" title="Description">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="Description6"></a>Description</h3>
</div>
</div>
</div>
<p>Definition from
<a class="ulink" href="http://en.wikipedia.org/wiki/Finite-state_machine" target="_new">Wikipedia</a>:
</p>
<div class="blockquote">
<blockquote class="blockquote">
<p>
A finite-state machine (FSM) or finite-state automaton (plural: automata), or simply a state machine, is a mathematical model used to design computer programs and digital logic circuits. It is conceived as an abstract machine that can be in one of a finite number of states. The machine is in only one state at a time; the state it is in at any given time is called the current state. It can change from one state to another when initiated by a triggering event or condition, this is called a transition. A particular FSM is defined by a list of the possible states it can transition to from each state, and the triggering condition for each transition.</p>
</blockquote>
</div>
<p>In ROOM each actor class can implement its behavior using a state machine. Events occurring at the end ports of an actor will be forwarded to and processed by the state machine. Events possibly trigger state transitions.</p>
</div>
<div class="section" title="Motivation">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="Motivation4"></a>Motivation</h3>
</div>
</div>
</div>
<p>For event driven systems a finite state machine is ideal for processing the stream of events. Typically during processing new events are produced which are sent to peer actors.</p>
<p>We distinguish flat and hierarchical state machines.</p>
</div>
<div class="section" title="Notation">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="Notation6"></a>Notation</h3>
</div>
</div>
</div>
<div class="section" title="Flat Finite State Machine">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="FlatFiniteStateMachine"></a>Flat Finite State Machine</h4>
</div>
</div>
</div>
<p>The simpler flat finite state machines are composed of the following elements:</p>
<table title="Title" frame="box" border="2" cellpadding="3" cellspacing="0" id="N11015">
<tr>
<td align="center">
<span class="bold"><strong>Description</strong></span></td>
<td align="center">
<span class="bold"><strong>Graphical Notation</strong></span></td>
<td align="center">
<span class="bold"><strong>Textual Notation</strong></span></td>
</tr>
<tr>
<td>State</td>
<td>
<div class="mediaobject">
<img src="images/040-State.jpg"></div>
</td>
<td>
<div class="mediaobject">
<img src="images/040-StateTextual.jpg"></div>
</td>
</tr>
<tr>
<td>InitialPoint</td>
<td>
<div class="mediaobject">
<img src="images/040-InitialPoint.jpg"></div>
</td>
<td>
<span class="emphasis"><em>implicit</em></span></td>
</tr>
<tr>
<td>TransitionPoint</td>
<td>
<div class="mediaobject">
<img src="images/040-TransitionPoint.jpg"></div>
</td>
<td>
<div class="mediaobject">
<img src="images/040-TransitionPointTextual.jpg"></div>
</td>
</tr>
<tr>
<td>ChoicePoint</td>
<td>
<div class="mediaobject">
<img src="images/040-ChoicePoint.jpg"></div>
</td>
<td>
<div class="mediaobject">
<img src="images/040-ChoicePointTextual.jpg"></div>
</td>
</tr>
<tr>
<td>Initial Transition</td>
<td>
<div class="mediaobject">
<img src="images/040-InitialTransition.jpg"></div>
</td>
<td>
<div class="mediaobject">
<img src="images/040-InitialTransitionTextual.jpg"></div>
</td>
</tr>
<tr>
<td>Triggered Transition</td>
<td>
<div class="mediaobject">
<img src="images/040-TriggeredTransition.jpg"></div>
</td>
<td>
<div class="mediaobject">
<img src="images/040-TriggeredTransitionTextual.jpg"></div>
</td>
</tr>
</table>
<p>
</p>
</div>
<div class="section" title="Hierarchical Finite State Machine">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="HierarchicalFiniteStateMachine"></a>Hierarchical Finite State Machine</h4>
</div>
</div>
</div>
<p>The hierarchical finite state machine adds the notion of a sub state machine nested in a state.
A few modeling elements are added to the set listed above:</p>
<table title="Title" frame="box" border="2" cellpadding="3" cellspacing="0" id="N110D4">
<tr>
<td align="center">
<span class="bold"><strong>Description</strong></span></td>
<td align="center">
<span class="bold"><strong>Graphical Notation</strong></span></td>
<td align="center">
<span class="bold"><strong>Textual Notation</strong></span></td>
</tr>
<tr>
<td>State with sub state machine</td>
<td>Parent State
<div class="mediaobject">
<img src="images/040-StateWithSubFSM.jpg"></div>
Sub state machine
<div class="mediaobject">
<img src="images/040-SubFSM.jpg"></div>
</td>
<td>
<div class="mediaobject">
<img src="images/040-StateWithSubFSMTextual.jpg"></div>
</td>
</tr>
<tr>
<td>Entry Point</td>
<td>In sub state machine
<div class="mediaobject">
<img src="images/040-EntryPoint.jpg"></div>
On parent state
<div class="mediaobject">
<img src="images/040-EntryPointRef.jpg"></div>
</td>
<td>
<div class="mediaobject">
<img src="images/040-EntryPointTextual.jpg"></div>
</td>
</tr>
<tr>
<td>Exit Point</td>
<td>In sub state machine
<div class="mediaobject">
<img src="images/040-ExitPoint.jpg"></div>
On parent state
<div class="mediaobject">
<img src="images/040-ExitPointRef.jpg"></div>
</td>
<td>
<div class="mediaobject">
<img src="images/040-ExitPointTextual.jpg"></div>
</td>
</tr>
</table>
<p>
</p>
</div>
</div>
<div class="section" title="Examples">
<div class="titlepage">
<div>
<div>
<h3 class="title">
<a name="Examples"></a>Examples</h3>
</div>
</div>
</div>
<div class="section" title="Example of a flat finite state machine:">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="Exampleofaflatfinitestatemachine"></a>Example of a flat finite state machine:</h4>
</div>
</div>
</div>
<p>
</p>
<div class="mediaobject">
<img src="images/040-FlatFSM.jpg"></div>
<p>
</p>
</div>
<div class="section" title="Example of a hierarchical finite state machine:">
<div class="titlepage">
<div>
<div>
<h4 class="title">
<a name="Exampleofahierarchicalfinitestatemachine"></a>Example of a hierarchical finite state machine:</h4>
</div>
</div>
</div>
<p>Top level
</p>
<div class="mediaobject">
<img src="images/040-HierarchicalFSMTop.jpg"></div>
<p>
</p>
<p>Sub state machine of Initializing
</p>
<div class="mediaobject">
<img src="images/040-HierarchicalFSMInitializing.jpg"></div>
<p>
</p>
<p>Sub state machine of Running
</p>
<div class="mediaobject">
<img src="images/040-HierarchicalFSMRunning.jpg"></div>
<p>
</p>
</div>
</div>
</div>
</body>
</html>
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