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PRISM Manual | ThePRISMLanguage / Introduction
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<p><a class='wikilink' href='Main.html'>The PRISM Language</a> /
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</p><h1>Introduction</h1>
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<p>In order to construct and analyse a model with PRISM,
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it must be specified in the PRISM language,
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a simple, state-based language,
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based on the Reactive Modules formalism of Alur and Henzinger [<a class='wikilink' href='../Main/References.html#AH99'>AH99</a>].
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This is used for all of the types of model that PRISM supports:
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discrete-time Markov chains (DTMCs),
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continuous-time Markov chains (CTMCs),
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Markov decision processes (MDPs)
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and probabilistic timed automata (PTAs).
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For background material on these models, look at the pointers to
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<a class='urllink' href='http://www.prismmodelchecker.org/about.php'>resources</a>
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on the PRISM web site.
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</p>
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<p class='vspace'>In this section, we describe the PRISM language and present a number of small illustrative examples.
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A precise definition of the semantics of the language is available from the "<a class='urllink' href='http://www.prismmodelchecker.org/doc/'>Documentation</a>" section of the PRISM web site. One of the best ways to learn what can be done with the PRISM language is to look at some existing examples.
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A number of these are included with the tool distribution in the <code>examples</code> directory.
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Many additional examples can be found on the "<a class='urllink' href='http://www.prismmodelchecker.org/casestudies/'>Case Studies</a>" section of the <a class='urllink' href='http://www.prismmodelchecker.org/'>PRISM website</a>.
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</p>
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<p class='vspace'>The fundamental components of the PRISM language are <em>modules</em> and <em>variables</em>.
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A model is composed of a number of <em>modules</em> which can interact with each other.
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A module contains a number of local <em>variables</em>.
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The values of these variables at any given time constitute the state of the module.
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The <em>global state</em> of the whole model is determined by the <em>local state</em> of all modules.
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The behaviour of each module is described by a set of <em>commands</em>.
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A command takes the form:
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<div class='vspace'></div>
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<div class='sourceblock ' id='sourceblock1'>
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<div class='sourceblocktext'><div class="prism">[] <span class="prismident">guard</span> -> <span class="prismident">prob_1</span> : <span class="prismident">update_1</span> + ... + <span class="prismident">prob_n</span> : <span class="prismident">update_n</span>;<br/>
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</div></div>
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<div class='sourceblocklink'><a href='http://www.prismmodelchecker.org/manual/ThePRISMLanguage/Introduction?action=sourceblock&num=1' type='text/plain'>[$[Get Code]]</a></div>
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</div>
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<p class='vspace'>The <em>guard</em> is a predicate over all the variables in the model (including those belonging to other modules). Each <em>update</em> describes a transition which the module can make if the guard is true. A transition is specified by giving the new values of the variables in the module, possibly as a function of other variables. Each update is also assigned a probability (or in some cases a rate) which will be assigned to the corresponding transition.
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<h3><a class='wikilink' href='../Main/Main.html'>PRISM Manual</a></h3>
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<p><strong><a class='wikilink' href='Main.html'>The PRISM Language</a></strong>
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</p><ul><li><a class='selflink' href='Main.html'>Introduction</a>
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</li><li><a class='wikilink' href='Example1.html'>Example 1</a>
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</li><li><a class='wikilink' href='ModelType.html'>Model Type</a>
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</li><li><a class='wikilink' href='ModulesAndVariables.html'>Modules And Variables</a>
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</li><li><a class='wikilink' href='Commands.html'>Commands</a>
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</li><li><a class='wikilink' href='ParallelComposition.html'>Parallel Composition</a>
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</li><li><a class='wikilink' href='LocalNondeterminism.html'>Local Nondeterminism</a>
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</li><li><a class='wikilink' href='CTMCs.html'>CTMCs</a>
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</li><li><a class='wikilink' href='Example2.html'>Example 2</a>
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</li><li><a class='wikilink' href='Constants.html'>Constants</a>
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</li><li><a class='wikilink' href='Expressions.html'>Expressions</a>
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</li><li><a class='wikilink' href='Synchronisation.html'>Synchronisation</a>
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</li><li><a class='wikilink' href='ModuleRenaming.html'>Module Renaming</a>
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</li><li><a class='wikilink' href='MultipleInitialStates.html'>Multiple Initial States</a>
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</li><li><a class='wikilink' href='GlobalVariables.html'>Global Variables</a>
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</li><li><a class='wikilink' href='FormulasAndLabels.html'>Formulas And Labels</a>
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</li><li><a class='wikilink' href='PTAs.html'>PTAs</a>
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</li><li><a class='wikilink' href='CostsAndRewards.html'>Costs And Rewards</a>
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</li><li><a class='wikilink' href='ProcessAlgebraOperators.html'>Process Algebra Operators</a>
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</li><li><a class='wikilink' href='PRISMModelFiles.html'>PRISM Model Files</a>
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</li></ul><p>[ <a class='wikilink' href='AllOnOnePage.html'>View all</a> ]
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