# petri - The Petri Net Method By Dr Chris Ling

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The Petri Net Method By Dr Chris Ling School of Computer Science & Software Engineering Monash University Chris.Ling@csse.monash.edu.au

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(C) Copyright 2001, Chris Ling Introduction First introduced by Carl Adam Petri in 1962. A diagrammatic tool to model concurrency and synchronization in distributed systems. Very similar to State Transition Diagrams. Used as a visual communication aid to model the system behaviour. Based on strong mathematical foundation.
(C) Copyright 2001, Chris Ling Example: EFTPOS System (STD of an FSM) Initial 1 digit 1 digit 1 digit 1 digit d1 d2 d3 d4 OK OK pressed approve Approved Rejected OK OK OK OK Initial state Final state Reject (EFTPOS= Electronic Fund Transfer Point of Sale)

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(C) Copyright 2001, Chris Ling Example: EFTPOS System (A Petri net) Initial 1 digit 1 digit 1 digit 1 digit d1 d2 d3 d4 OK OK approve approved OK OK OK OK Reject Rejected!
(C) Copyright 2001, Chris Ling EFTPOS System Scenario 1: Normal Enters all 4 digits and press OK. Scenario 2: Exceptional Enters only 3 digits and press OK.

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(C) Copyright 2001, Chris Ling Example: EFTPOS System (Token Games) Initial 1 digit 1 digit 1 digit 1 digit d1 d2 d3 d4 OK OK approve approved OK OK OK OK Reject Rejected!
(C) Copyright 2001, Chris Ling A Petri Net Specification . .. consists of three types of components: places (circles), transitions (rectangles) and arcs (arrows): Places represent possible states of the system; Transitions are events or actions which cause the change of state; And Every arc simply connects a place with a transition or a transition with a place.

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(C) Copyright 2001, Chris Ling A Change of State … is denoted by a movement of token(s) (black dots) from place(s) to place(s); and is caused by the firing of a transition. The firing represents an occurrence of the event or an action taken. The firing is subject to the input conditions, denoted by token availability.
(C) Copyright 2001, Chris Ling A Change of State A transition is firable or enabled when there are sufficient tokens in its input places. After firing, tokens will be transferred from the input places (old state) to the output places, denoting the new state.

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## This note was uploaded on 12/12/2009 for the course SE 3306 taught by Professor Nhut during the Spring '09 term at University of Texas at Dallas, Richardson.

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petri - The Petri Net Method By Dr Chris Ling

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