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[Jen92] Kurt Jensen. Coloured Petri Nets. Basic Concepts, Analysis Methods and Practical Use. Volume 1. Springer-Verlag. 1992.
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paper_books/. 1997
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[The97] Theo van Drimmelen. Implementation of Statistical Functions in Design/CPN.
http://www.daimi.aau.dk/designCPN/libs/pdf. 1997.
171
LouiseLorentsen
DepartmentofComputerScience
UniversityofAarhus
NyMunkegade,Bldg.540
DK-8000AarhusC,Denmark
E-mail:louisel@daimi.au.dk
Abstract. Inthis paperthepractical use ofColoured PetriNets and Design/CPN isdemonstrated
through an industrial cooperation project. The project is based on studies of a concrete industrial
productandonmethodswell-knownandcurrentlyusedinthedesignoftheproductinthecompany.
ThepaperdescribesthemodellinginDesign/CPNofthesystemoftheproductfollowedbyananalysis
of the model in relation to a set of desired properties dened by the company. The properties are
formallyveriedbymeansofoccurrencegraphsandtheDesign/CPNOccurrenceGraphtool.
1 Introduction
ThispaperisbasedonaprojectintheCentreforObjectTechnology(COT),whichisajointprojectbetween
industryand universities in Denmark. The projectis acooperation projectbetweentheDanish industrial
productioncompanyDanfossandtheCPNgroupatUniversityofAarhus.Threepersons,representingboth
sides, have been involved in the projectas primary project memberssupported by the leaders from both
cooperating parties. The project group has held a number of meetings and communicated electronically
throughout the whole project. However, most work has been based on internal documents kindly made
availablefortheprojectbythecompany.
Theoverallaim ofthepaper,andthe underlyingproject,istoshowtheapplicabilityof ColouredPetri
Nets(CPNs)[7]andoccurrencegraphs(OGs)[6]inindustrialsettings.Inordertosucceedinthisendeavourit
isimportanttorelatetoconcreteindustrialproductsononehandandtothesolutionsusedsofarinindustry
onthe other hand.Inthe project,which this paperisbased on,this means that aspecic productof the
cooperatingindustrial company,aowmeter(Fig.1), ischosenasarelevantstudy object,andthatpresent
design techniquesof this system is related to and combinedwith the new design and analysis techniques
basedonCPNsandOGs.
Fig.1.Aowmeter
Flowmetersareprimarily usedformeasuringtheowofwaterthroughpipes.Intheconcreteowmeter
systemofthis projectdierentprocessesare usedtomeasure theow,e.g.,aowmeasurementprocess,a
temperature measurementprocess and acalculation process. These processescooperatesto carry outthe
overalltask-tomeasuretheowofwaterin thepipe.
173
operatingsystemtoadistributed andmoreexiblesystemwith hardwaremodules whichcanbecombined
in many ways. With the new distributed owmeter system a customer can design his own system and
construct it from only the needed modules. However, this makes new problems arise. In the distributed
settingbasedoncommunicationbetweentheprocessesitisdiÆculttoreasonabouttheindividualprocesses
andtheirinuenceoneachother.
Practicaltests inDanfosshaveshownthat theprocesscommunicationinthe rstdesignversionofthe
owmeter system containedat least onedeadlock, and therefore anewdesign wasneeded. As partof the
newdesignaset ofdesiredpropertiesofaowmetersystemhavebeenformulatedandasolutionhasbeen
presentedusingnewdesignmethods,butthecorrectnessofthesolutionstillhastobeformallyveried.This
projectshouldbeseenaspartoftheseexperimentswithnewmethodsinDanfoss.Theaimoftheunderlying
project has been to secure the quality of the design process in Danfoss introducing Coloured Petri Nets
(CPNsorCP-nets) andthetoolDesign/CPN[3].
In the following the owmeter system is described in more detail, a CPN model of the protocol is
introduced, a set of desired properties of the owmeter system are motivated and formulated, dierent
designalternativesfortheprocessesaremodelledinDesign/CPNanditisanalysedbymeansofoccurrence
graphsusingtheDesign/CPNOG tool[8] whetherthedesignalternativesfull thedesiredpropertiesofa
owmeter system.
2 The owmeter system
TheowmetersystemconsistsofoneormoremodulesconnectedviaaControllerAreaNetwork(CAN)[9].
TheprocessesarecalledCANApplications(CANAPPs)andareplacedinthemodules.Theplacementofthe
CANAPPsinthemodulesisexible, however,whichmeansthat theconcreteplacementoftheCANAPPs
shouldnotaect thefunctionalityofthetotalsystem.Allcommunicationinthesystemconsistsofmessage
passing between the CANAPPs. To control the communication among the CANAPPs in the modules a
superior communication system is needed. The communication system consists of parts in every module
calleddrivers.Thismeansthataowmetersystemconsistsofanumberofmodules,eachcontainingadriver
andoneormoreCANAPPs.AsystemofthreemoduleseachcontainingfourCANAPPsisshowninFig.2.
Inthefollowingtheprotocoldeningthetransactionprocedure andmessagestructureispresented.
CANAPP Module
CANAPP Module
driver
driver CANAPP
driver
Module
CAN
Fig.2.Aowmetersystem
2.1 The protocol
Theprotocolisbasedonathreelayeredarchitecture.ThelayersconstituteacollapsedformoftheOSIseven
layerarchitecture,mappingontothephysical,datalink andapplicationlayersof theOSIReferenceModel
[4].
inFig.3.Theservicesfallinto twogroups,whichwillbedealt withseparatelyinthefollowingdescription:
two-wayasynchronouscommunicationandone-wayasynchronouscommunication.
Service Function
read AddressanotherCANAPPandreadthevalueofanattribute
write AddressanotherCANAPPandmodifythevalueofanattribute
action AddressanotherCANAPPandaskittoexecuteanaction
broadcastCyclicallydistributionofactualvalueswithoutanyacknowledgements
commandAddressallotherCANAPPsandaskthemtoexecuteasystemcommand
event AddressallotherCANAPPsandreportasingleevent
Fig.3.Theapplicationlayerservices
The system considered in the rest of this section is a system of three modules each containing one
CANAPP.Thesystemisshownin Fig.4.