DEMO CPN-tools

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DEMOCPN-tools

• Ronny Mans
• Eindhoven University of Technology, Faculty of
  Technology Management,
• Department of Information Systems, P.O.Box 513,
  NL-5600 MB,
• Eindhoven, The Netherlands.

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Outline

• Introduction to CPN Tools
• Building a net
• Time, Hierarchy and Color
• Analysis
• Simulation
• Single run, replications
• Monitors
• Net for DCT case

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Classical Petri net

• Simple process model
• Just three elements places, transitions and
  arcs.
• Graphical and mathematical description.
• Formal semantics allows for analysis.

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Limitations of classical Petri nets

• Inability to test for zero tokens in a place.
• Models tend to become large.
• Models cannot reflect temporal aspects
• No support for structuring large models, cf.
  top-down and bottom-up design
• High level Petri nets in CPN
• Color
• Time
• Hierarchy

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CPN (Colored Petri nets)

• CPN is the language developed by Kurt Jensen.
• CPN supports the extensions with time, color and
  hierarchy.
• CPN is based on standard ML.
• CPN is supported by Design/CPN and CPN Tools.
• For more information http//www.daimi.au.dk/CPnet
  s/

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Simulations

• Simulations of CP-nets are run for many reasons
• Debugging
• Analysis of system behavior (performance or
  functional)
• Presentation of a model to project team
• Communication with external programs
• The usefulness of the simulations is heavily
  dependent on the flexibility and functionality of
  the simulator.
• Access to simulation information
• Stopping simulations

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Accessing simulation information

• It is often useful to be able to exchange
  information between the CPN simulator and
  external processes or files.
• Code segments can be added to transitions for
• Reading and writing in files
• Calculating some performance measures
• Sending and receiving information from external
  processes

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Controlling a simulation

• Simulation stop criteria
• Number of steps executed
• Dependent on model time
• Dependent on markings or transitions

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Common functionality

• These controlling and accessing activities share
  a common pattern If certain conditions are
  fulfilled, then do something.
• If transition T occurs, then save information in
  a file.
• If there are no tokens on place P, then stop the
  simulation.
• If model time is greater than C, then calculate
  the average number of tokens on place P.

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Problems when simulating

• Problems controlling and accessing simulation
  information
• Cannot access marking information.
• Net structure may have to be changed to obtain
  desired functionality.
• If multiple transitions need to be inspected,
  then code segments must be duplicated.
• Code segments cannot be disabled.
• Only low-level support, which is difficult to use.

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Monitors in CPN Tools

• monitor (verb) to watch, keep track of, or check,
  usually for a special purpose
• Merriam-Websters Collegiate Dictionary
• A monitor is a mechanism that is used to observe,
  inspect, control or modify a simulation of a
  CP-net.
• Important characteristics of monitors
• They can inspect the states and events of a
  simulation, and take appropriate actions based on
  the observations.
• There is an explicit separation between
  monitoring the behavior of a net, and modeling
  the behavior of the system.

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Levels of monitors

• Standard monitors
• Very easy to define
• Do not require users to write any code
• Parameterized monitors
• Similar to standard monitors, but slightly more
  flexible, and require some programming
• User-defined monitors
• Very flexible, but require more programming

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Monitoring subnets

• A monitor can inspect markings and occurring
  transitions, with variable bindings, during a
  simulation
• Zero or more places
• Zero or more transitions
• Monitors are activated after simulation steps
• After every simulation step, if no transitions
  are monitored
• After every relevant transition has occurred

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Data Collector monitors

• Mark Size (used on places)
• List Length Data Collector (used on places)
• Count Transition (used on
  transitions)
• Generic Data Collector (used on subnets)

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Breakpoint monitors

• Place Content (used on places)
• Transition Enabled (used on transitions)
• Generic Breakpoint (used on subnets)

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Other monitors

• Write in file (used on subnets)
• User defined (used on subnets)

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Monitoring functions

• Initialization function
• Called once before a simulation
• Predicate function
• Called after simulation steps
• Observation function
• Called when predicate function returns true
• Extracts relevant data from the model
• Action function
• Does something appropriate with the observed
  value
• Stop function
• Called once after a simulation

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• Questions?