Petri Net Markup Language(PNML)

Nickolas PaladinoOct. 9, 2002

University of Central Florida

Outline

• PNML History

• Considerations for Standard

• Specification

• Example Petri Net

• Sample PNML

Outline

• Application

• Deficiencies

• Current State

• Future Direction

• Conclusion

• References

PNML History

• Petri Net Tools - variety

e.g. Artifex, CPN-AMI, HiQPN-Tool, Renew, PACE

• Each has unique internal representation and saved/exported file format definition

PNML History

• Reasons to move to a standard

- Useful to move Net Models from tool to tool, not redesign from scratch

- Make available libraries or toolkits of predefined Petri Net pieces

- Moving project to different tool obsolete tool, stronger analysis, better graphics capability

PNML History

• Obstacles to a standard

- Additional development by tool designers

- don’t want to loose advanced features specific to any tool

- problems with extensibility

e.g. Java – Sun vs Microsoft, HTML – Netscape vs Microsoft

Considerations for Standard

• Standard should be:

- simple

- include only necessary technology

• Reference parsers should be available

• Need converters from old formats

• Experience from tool developers

Considerations for Standard

• Why XML (Extensible Mark-up Language)?

- able to use robust parsers

- large choice of XML tools

- flexible, for easy extension of formats

- parsers can ignore unknown parts

Specification

• ISO 15909

High-level Petri Nets – Concepts, Definitions and Graphical Notation

Final Draft Version 4.7.1

October 28, 2000

Sample Petri NetInput

Ready

Output

Idle

Resource

Get Next Item

Process Item

InItem

iitem

(iitem ,m )

m

m

M

MIxM

(iitem ,m )

oitem

OutItem

R

r

Sample PNML

• Sytle Sheet CSS Syntax

place { shape: ellipse; }

place name { font-size 12pt; }

transition { shape : box }

transition name { font-size: 11pt; }

Sample PNML

• Entities extended with class information

<place id="input" class="material-flow"> <name>Input</name>

<type>InItem</type>

</place>

<arc id="a1">

<placeend idref="input" class="material-flow">

<transend idref="get-next-item">

</arc>

<transition id="get-next-item" class="material-flow">

<name>Get Next Item</name>

</transition>

Sample PNML

• Petri Net mathematical description

<pn> <place id="input"> <name>Input</name> <type>InItem</type> </place>

<arc id="a1"> <placeend idref="input"> <transend idref="get-next-item"> <expr>iitem</expr> </arc>

<transition id="get-next-item"> <name>Get Next Item</name> </transition>

<place id="idle"> <name>Idle</name> <type>M</type> <initmark>M</initmark> </place>

<arc id="a2"> <placeend idref="idle"> <transend idref="get-next-item"> <expr>m</expr> </arc>

...

</pn>

Sample PNML

• Petri Net layout description

<layout> <node ref="machine.pn#input"> <coord> <x>10.0</x> <y>0.0</y> </coord> </node>

<conn ref="machine.pn#a1"> <!-- no bend points -->

<node ref="machine.pn#get-next-item"> <coord> <x>10.0</x> <y>10.0</y> </coord> </node>

<node ref="machine.pn#idle"> <coord> <x>20.0</x> <y>20.0</y> </coord> </node>

<conn ref="machine.pn#a2"> <coord> <x>20.0</x> <y>10.0</y> </coord> </conn>

...

</layout>

Application

• Must communicate adequate detail of Petri Net DefinitionHold meaning of common notations

Extend for special features of varied tools

• Allows Petri Net use on different toolsVaried strengths and weaknesses of tools

e.g. initial design, simulation, editing, analysis, GUI

Deficiencies

• Petri Nets graphical in natureDifficult to capture same look across existing applications

• Petri Nets can become very large

• Many existing Petri Net toolsRetrofit of each can be time consuming and has cost

Converters from old standards needed

Current State

• The Petri Net Interchange Format Mailing List

http://www.informatik.hu-berlin.de/top/PNX/

Little activity

One comment since 2000

• Some tools have moved to XML-based file format

Future Direction

• Should not force developers to use PNML

• Standards committee to make format freely available

• Current tools could begin to use own XML, converge to PNML

Conclusion

• Correct direction to pursue

• Needed by academia and industry

• Will eventually be adopted

• No technical problems in XML based PNML definitions

• Agree on standard and move to implement

References

• [Mai00] Mailund, Thomas (2000). Seperation of Style and Content with XML in an Interchange Format for High-level Petri Nets (Mailund, T. , Mortensen, K. H.),   Position Paper, 21st International Conference on Application and Theory of Petri Nets Aarhus (2000)

• [Kum00] Kummer, Olaf (2000). XML and Petri Nets – Following the Forces (Kummer, O., Wienberg, F., Moldt, D.),  Position Paper, 21st International Conference on Application and Theory of Petri Nets Aarhus (2000)

• [Mat00] Matthias, Jungel (2000). Towards a Generic Interchange Format for Petri Nets (Matthias, J., Kindler, E., Weber, M.),  Position Paper, 21st International Conference on Application and Theory of Petri Nets Aarhus (2000)

References (WWW)

• The PNK Team: Petri Net Markup Language. http://www.informatic.hu-berlin.ed/top/pnml/. Aug. 2002.

• Petri Net Tools and Software. http://www.daimi.aau.dk/PetriNets/tools/. Oct. 2002.

• 21st International Conference on Application and Theory of Petri Nets. http://www.daimi.au.dk/pn2000/Interchange/. June 2000.