Analysis techniques for dependability - Petri net techniques

This International Standard provides guidance on a Petri net based methodology for dependability purposes. It supports modelling a system, analysing the model and presenting the analysis results. This methodology is oriented to dependability-related measures with all the related features, such as reliability, availability, production availability, maintainability and safety (e.g. safety integrity level (SIL) [2] related measures). This standard deals with the following topics in relation to Petri nets: a) defining the essential terms and symbols and describing their usage and methods of graphical representation; b) outlining the terminology and its relation to dependability; c) presenting a step-by-step approach for 1) dependability modelling with Petri nets, 2) guiding the usage of Petri net based techniques for qualitative and quantitative dependability analyses, 3) representing and interpreting the analysis results; d) outlining the relationship of Petri nets to other modelling techniques; e) providing practical examples. This standard does not give guidance on how to solve mathematical problems that arise when analysing a PN; such guidance can be found in [3] and [4]. This standard is applicable to all industries where qualitative and quantitative dependability analyses is performed.

Analysemethoden für Zuverlässigkeit - Petrinetze

Techniques d'analyse de sûreté de fonctionnement - Techniques des réseaux de Petri

La CEI 62551:2012 donne des directives pour une technique basée sur les réseaux de Petri dans le domaine de la sûreté de fonctionnement. Elle porte sur la modélisation d'un système, l'analyse du modèle et la présentation des résultats de l'analyse. Cette méthode est orientée vers les mesures relatives à la sûreté de fonctionnement avec toutes les caractéristiques associées, telles que la fiabilité, la disponibilité, la disponibilité de production, la maintenabilité et la sécurité (par exemple, les mesures associées au niveau d'intégrité de sécurité (SIL[2]: en anglais:system integrity level). Mots clés: technique basée sur les réseaux de Petri dans le domaine de la sûreté de fonctionnement

Tehnike analize zagotovljivosti - Tehnike Petrijeve mreže

Ta mednarodni standard podaja smernice o metodologiji, ki temelji na Petrijevi mreži, za namene zagotovljivosti. Podpira modeliranje sistema, analizo modela in predstavitev rezultatov analize. Ta metodologija je usmerjena v ukrepe v zvezi z zagotovljivostjo z vsemi zadevnimi lastnostmi, kot je zanesljivost, razpoložljivost, razpoložljivost proizvodnje, sposobnost vzdrževanja in varnost (npr. ukrepi v zvezi z 2. stopnjo varnostne celovitosti (SIL)). Ta standard obravnava naslednje teme na področju Petrijevih mrež: a) opredelitev bistvenih izrazov in simbolov ter opis njihove uporabe in metod za grafično predstavitev; b) pregled terminologije in njene povezave z zagotovljivostjo; c) predstavitev načela postopnosti za 1) modeliranje zagotovljivosti s Petrijevimi mrežami, 2) navodila za uporabo tehnik, ki temeljijo na Petrijevi mreži, za kvalitativne in kvantitativne analize zagotovljivosti, 3) predstavitev in razlaganje rezultatov analize; d) opis povezave med Petrijevimi mrežami in drugimi tehnikami modeliranja; e) navedbo praktičnih primerov. Ta standard ne podaja smernic za reševanje matematičnih problemov, ki nastanejo pri analizi Petrijeve mreže; take smernice so navedene v točkah [3] in [4]. Ta standard se uporablja v vseh industrijah, v katerih se izvajajo kvalitativne in kvantitativne analize zagotovljivosti.

General Information

Status
Published
Publication Date
21-Jan-2013
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
11-Jan-2013
Due Date
18-Mar-2013
Completion Date
22-Jan-2013

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SLOVENSKI STANDARD
SIST EN 62551:2013
01-marec-2013
Tehnike analize zagotovljivosti - Tehnike Petrijeve mreže
Analysis techniques for dependability - Petri net techniques

Techniques d'analyse de sûreté de fonctionnement - Techniques des réseaux de Petri

Ta slovenski standard je istoveten z: EN 62551:2012
ICS:
21.020 =QDþLOQRVWLLQQDþUWRYDQMH Characteristics and design of
VWURMHYDSDUDWRYRSUHPH machines, apparatus,
equipment
SIST EN 62551:2013 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 62551:2013
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SIST EN 62551:2013
EUROPEAN STANDARD
EN 62551
NORME EUROPÉENNE
November 2012
EUROPÄISCHE NORM
ICS 21.020
English version
Analysis techniques for dependability -
Petri net techniques
(IEC 62551:2012)
Techniques d'analyse de sûreté de Analysemethoden für Zuverlässigkeit -
fonctionnement - Petrinetze
Techniques des réseaux de Petri (IEC 62551:2012)
(CEI 62551:2012)

This European Standard was approved by CENELEC on 2012-11-06. CENELEC members are bound to comply

with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard

the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on

application to the CEN-CENELEC Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CENELEC member into its own language and notified

to the CEN-CENELEC Management Centre has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,

the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany,

Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland,

Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2012 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 62551:2012 E
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SIST EN 62551:2013
EN 62551:2012 - 2 -
Foreword

The text of document 56/1476/FDIS, future edition 1 of IEC 62551, prepared by IEC/TC 56

"Dependability" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as

EN 62551:2012.
The following dates are fixed:
(dop) 2013-08-06
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2015-11-06
• latest date by which the national
standards conflicting with the
document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such

patent rights.
Endorsement notice

The text of the International Standard IEC 62551:2012 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 61508 Series NOTE Harmonised as EN 61508 Series (not modified).
IEC 61508-4:2010 NOTE Harmonised as EN 61508-4:2010 (not modified).
IEC 61508-1:2010 NOTE Harmonised as EN 61508-1:2010 (not modified).
IEC 61165:2006 NOTE Harmonised as EN 61165:2006 (not modified).
IEC 60812:2006 NOTE Harmonised as EN 60812:2006 (not modified).
IEC 61025:2006 NOTE Harmonised as EN 61025:2007 (not modified).
IEC 61078:2006 NOTE Harmonised as EN 61078:2006 (not modified).
IEC 61511-3:2003 NOTE Harmonised as EN 61511-3:2004 (not modified).
IEC 61703:2001 NOTE Harmonised as EN 61703:2002 (not modified).
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SIST EN 62551:2013
- 3 - EN 62551:2012
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD

applies.
Publication Year Title EN/HD Year
IEC 60050-191 1990 International Electrotechnical Vocabulary - -
(IEV) -
Chapter 191: Dependability and quality
of service
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SIST EN 62551:2013
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SIST EN 62551:2013
IEC 62551
Edition 1.0 2012-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Analysis techniques for dependability – Petri net techniques
Techniques d'analyse de sûreté de fonctionnement – Techniques des réseaux
de Petri
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XB
ICS 21.020 ISBN 978-2-83220-370-5

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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SIST EN 62551:2013
– 2 – 62551 © IEC:2012
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope ............................................................................................................................... 8

2 Normative references ....................................................................................................... 8

3 Terms, definitions, symbols and abbreviations .................................................................. 8

3.1 Terms and definitions .............................................................................................. 8

3.2 Symbols and abbreviations .................................................................................... 10

4 General description of Petri nets .................................................................................... 12

4.1 Untimed low-level Petri nets .................................................................................. 12

4.2 Timed low-level Petri nets ..................................................................................... 12

4.3 High-level Petri nets .............................................................................................. 13

4.4 Extensions of Petri nets and modelling with Petri nets ........................................... 13

4.4.1 Further representations of Petri net elements ............................................ 13

4.4.2 Relationship to the concepts of dependability ............................................ 14

5 Petri net dependability modelling and analysis................................................................ 15

5.1 The steps to be performed in general .................................................................... 15

5.2 Steps to be performed in detail .............................................................................. 16

5.2.1 General ..................................................................................................... 16

5.2.2 Description of main parts and functions of the system (Step 1) .................. 16

5.2.3 Modelling the structure of the system on the basis of Petri net-

submodels and their relations (Step 2)....................................................... 16

5.2.4 Refining the models of Step 2 until the required level of detail is

achieved (Step 3) ...................................................................................... 18

5.2.5 Analysing the model to achieve the results of interest (Step 4) .................. 18

5.2.6 Representation and interpretation of results of analyses (Step 5) .............. 19

5.2.7 Summary of documentation (Step 6) .......................................................... 20

6 Relationship to other dependability models ..................................................................... 20

Annex A (informative) Structure and dynamics of Petri nets ................................................. 22

Annex B (informative) Availability with redundancy m-out-of-n ............................................. 33

Annex C (informative) Abstract example .............................................................................. 39

Annex D (informative) Modelling typical dependability concepts ........................................... 43

Annex E (informative) Level-crossing example ..................................................................... 45

Bibliography .......................................................................................................................... 62

Figure 1 – Weighted inhibitor arc .......................................................................................... 13

Figure 2 – Place p is a multiple place .................................................................................... 14

Figure 3 – Marking on p after firing of transition t .................................................................. 14

Figure 4 – The activation of t depends on the value of V ....................................................... 14

Figure 5 – Methodology consisting mainly of ‘modelling’, ‘analysing’ and ‘representing’

steps..................................................................................................................................... 15

Figure 6 – Process for dependability modelling and analysing with Petri nets ....................... 15

Figure 7 – Modelling structure concerning the two main parts 'plant' and 'control' with

models for their functions and dependability ......................................................................... 17

Figure 8 – Indication of the analysis method as a function of the PN model .......................... 19

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SIST EN 62551:2013
62551 © IEC:2012 – 3 –

Figure A.1 – Availability state-transition circle of a component .............................................. 22

Figure A.2 – Transition ‘failure’ is enabled ............................................................................ 23

Figure A.3 – ‘Faulty’ place marked due to firing of ‘failure' ................................................... 23

Figure A.4 – Transition ‘comp repair’ is enabled .................................................................. 24

Figure A.5 – The token at the ‘maintenance crew available’ location is not used ................... 24

Figure A.6 – Transition is not enabled ................................................................................... 25

Figure A.7 – Marking before firing ......................................................................................... 25

Figure A.8 – Marking after firing ............................................................................................ 25

Figure A.9 – PN with initial marking ...................................................................................... 25

Figure A.10 – Corresponding RG .......................................................................................... 25

Figure A.11 – Transitions ‘comp repair’ and ‘comp failure’ are enabled .......................... 26

lp hp

Figure A.12 – Marking after firing of transition ‘comp repair’ ............................................... 27

Figure A.13 – A timed PN with two exponentially distributed timed transitions ....................... 28

Figure A.14 – The corresponding stochastic reachability graph ............................................. 28

Figure A.15 – Petri net with timed transitions ........................................................................ 29

Figure B.1 – Two individual item availability nets with specific failure- and repair-rates ......... 33

Figure B.2 – Stochastic reachability graph corresponding to Figure B.1 with global

states (as an abbreviation c is used for “comp faulty”) ............................................................. 33

1 1

Figure B.3 – Three individual item availability nets with specific failure rates and repair

rates ..................................................................................................................................... 33

Figure B.4 – Stochastic reachability graph corresponding to Figure B.3 with global

states (as an abbreviation c is used for ‘comp faulty’) ....................................................... 34

Figure B.5 – Specifically connected 1-out-of-3 availability net ............................................... 35

Figure B.6 – Specifically connected 2-out-of-3 availability net ............................................... 35

Figure B.7 – Specifically connected 3-out-of-3 availability net ............................................... 36

Figure B.8 – Stochastic reachability graph with system specific operating states .................. 36

Figure B.9 – Specifically connected 1-out-of-3 reliability net ................................................ 37

Figure B.10 – Reachability graph for the net in Figure B.9 ................................................... 37

Figure B.11 – Specifically connected 2-out-of-3 reliability net .............................................. 37

Figure B.12 – Reachability graph for the net in Figure B.11 ................................................. 37

Figure B.13 – Specifically connected 3-out-of-3 reliability net .............................................. 38

Figure B.14 – Reachability graph for the net in Figure B.13 ................................................. 38

Figure C.1 – Individual availability net ................................................................................... 39

Figure C.2 – Stochastic availability graph of the net in Figure C.1 with its global states

and aggregated global states according to availability and safety ........................................ 39

Figure C.3 – Basic reliability and function modelling concept ................................................ 40

Figure C.4 – General hierarchical net with supertransitions to model reliability ..................... 41

Figure C.5 – General hierarchical net with supertransitions and superplaces ........................ 41

Figure C.6 – General hierarchical net with supertransitions to model availability ................... 41

Figure C.7 – General hierarchical net with supertransitions and superplaces ........................ 42

Figure E.1 – Applied example of a level crossing and its protection system .......................... 45

Figure E.2 – Main parts of the level crossing example model ................................................ 46

Figure E.3 – Submodels of the level crossing example model ............................................... 47

Figure E.4 – PN model of car and train traffic processes ....................................................... 48

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SIST EN 62551:2013
– 4 – 62551 © IEC:2012

Figure E.5 – PN model of the traffic processes and traffic dependability ............................... 49

Figure E.6 – PN model of the traffic process with an ideal control function ............................ 50

Figure E.7 – PN model of the level crossing example model ................................................. 51

Figure E.8 – Collected measures of the road traffic flow of a particular level crossing:

Time intervals between two cars coming to the level crossing ............................................... 52

Figure E.9 – Approximated probability distribution function based on the measures

depicted in Figure E.5 ........................................................................................................... 53

Figure E.10 – Collected measurements of time spent by road vehicle in the danger

zone of the level crossing ..................................................................................................... 53

Figure E.11 – Approximated probability distribution function based on measurements

depicted in Figure E.10 ......................................................................................................... 54

Figure E.12 – Aggregated RG and information about the corresponding states ..................... 59

Figure E.13 – Results of the quantitative analysis showing the level crossing average

availability for road traffic users as a function of the protection equipment hazard rate

for different used activation and approaching times T ........................................................ 60

Figure E.14 – Results of the quantitative analysis showing the individual risk of the

level crossing users as a function of the protection equipment hazard rate for different

used activation and approaching times T ........................................................................... 60

Figure E.15 – Availability safety diagram based on the quantitative results of the model

analysis shown in Figure E.13 and Figure E.14 ..................................................................... 61

Table 1 – Symbols in untimed Petri nets ............................................................................... 10

Table 2 – Additional symbols in timed Petri nets ................................................................... 11

Table 3 – Symbols for hierarchical modelling ........................................................................ 11

Table 4 – Corresponding concepts in systems, Petri nets and dependability ......................... 15

Table 5 – Mandatory and recommended parts of documentation ........................................... 20

Table A.1 – Corresponding concepts in systems, Petri nets, reachability graphs and

dependability ........................................................................................................................ 26

Table A.2 – Place and transition with rewards ....................................................................... 32

Table D.1 – Dependability concepts modelled with PN structures ......................................... 43

Table D.2 – Modelling costs of states and events.................................................................. 44

Table E.1 – Car-related places in the submodel ‘Traffic process’ (see Figure E.4) ................ 52

Table E.2 – Car-traffic related transitions in the submodel ‘Traffic process’ and Traffic

dependability (see Figure E.7) .............................................................................................. 55

Table E.3 – Train-traffic related places in the submodel ‘Traffic process’ (see

Figure E.7) ............................................................................................................................ 55

Table E.4 – Train-traffic related transitions in the submodel ‘Traffic process’ (see

Figure E.7) ............................................................................................................................ 56

Table E.5 – Places in the submodel ‘Traffic dependability’ (see Figure E.7) .......................... 56

Table E.6 – Transitions in the submodel ‘Traffic dependability’ (see Figure E.7) ................... 56

Table E.7 – Places in the submodel ‘Control function’ (see Figure E.7) ................................. 57

Table E.8 – Transitions in the submodel ‘Control function’ (see Figure E.7) .......................... 57

Table E.9 – Places in the submodel ‘Control equipment dependability’ (see Figure E.7) ....... 57

Table E.10 – Transitions in the submodel ‘Control equipment dependability’ (see

Figure E.7) ............................................................................................................................ 58

Table E.11 – Specification of boolean conditions for states to be subsumed in an

aggregated state ................................................................................................................... 59

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SIST EN 62551:2013
62551 © IEC:2012 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ANALYSIS TECHNIQUES FOR DEPENDABILITY –
PETRI NET TECHNIQUES
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

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consensus of opinion on the relevant subjects since each technical committee has representation from all

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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

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6) All users should ensure that they have the latest edition of this publication.

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members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62551 has been prepared by committee 56: Dependability.

The text of this standard is based on the following documents:
FDIS Report on voting
56/1476/FDIS 56/1484/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

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SIST EN 62551:2013
– 6 – 62551 © IEC:2012

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
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SIST EN 62551:2013
62551 © IEC:2012 – 7 –
INTRODUCTION

This International Standard provides a basic methodology for the representation of the basic

elements of Petri nets (PNs) [1] and provides guidance for application of the techniques in

the dependability field.

The inherent power of Petri net modelling is its ability to describe the behaviour of a system

by modelling the relationship between local states and local events. Against this background,

Petri nets have gained widespread acceptance in many industrial fields of application (e.g.

information, communication, transportation, production, processing and manufacturing and

power engineering).

The conventional methods are very limited when dealing with actual industrial systems

because they are neither able to handle multi-state systems, nor able to model dynamic

system behaviour (e.g. fault tree or reliability Block diagrams), and can be subject to the

combinatory explosion of the states to be handled (e.g. Markov process). Therefore,

alternative modelling and calculating methods are needed.

Dependability calculations of an industrial system intend to model the various states of the

system and how it evolves from one state to another when events (failures, repairs, periodic

tests, night, day, etc.) occur.

Reliability engineers need a user-friendly graphical support to achieve their models. Due to

their graphical presentation, Petri nets are a very promising modelling technique for

dependability modelling and calculations.

Analytical calculations are limited to small systems and/or by strong hypothesis (e.g.

exponential laws, low probabilities) to be fulfilled. A qualitative increase is needed to deal with

industrial size systems. This may be done by going from analytical calculation to Monte Carlo

simulation.

This standard aims at defining the consolidated basic principles of the PNs in the context of

dependability and the current usage of Petri net PN modelling and analysing as a means for

qualitatively and quantitatively assessing the dependability and risk-related measures of a

system.
—————————
Figures in square brackets refer to the bibliography.
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SIST EN 62551:2013
– 8 – 62551 © IEC:2012
ANALYSIS TECHNIQUES FOR DEPENDABILITY –
PETRI NET TECHNIQUES
1 Scope

This International Standard provides guidance on a Petri net based methodology for

dependability purposes. It supports modelling a system, analysing the model and presenting

the analysis results. This methodology is oriented to dependability-related measures with all

the related features, such as reliability, availability, production availability, maintainability and

safety (e.g. safety integrity level (SIL) [2] related measures).
This standard deals with the following topics in relation to Petri nets:

a) defining the essential terms and symbols and describing their usage and methods of

graphical representation;
b) outlining the terminology and its relation to dependability;
c) presenting a step-by-step approach for
1) dependability modelling with Petri nets,

2) guiding the usage of Petri net based techniques for qualitative and quantitative

dependability analyses,
3) representing and interpreting the analysis results;
d) outlining the relationship of Petri nets to other modelling techniques;
e) providing practical examples.

This standard does not give guidance on how to solve mathematical problems that arise when

analysing a PN; such guidance can be found in [3] and [4].

This standard is applicable to all industries where qualitative and quantitative dependability

analyses is performed.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

...

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