BPEL2oWFN User's Manual


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About this document:

This manual is for BPEL2oWFN, Version 1.2, a tool translating a web service described in BPEL into an open workflow net (oWFN), last updated 6 April 2006. This manual does not explain how to setup or install BPEL2oWFN. For this information please read the Installation Manual which is part of the distribution or can be downloaded from the website of BPEL2oWFN (http://www.informatik.hu-berlin.de/top/tools4bpel/bpel2owfn).

Copyright © 2005, 2006 Niels Lohmann

Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.

BPEL2oWFN is licensed under the GNU General Public License.

Copyright © 2005, 2006 Niels Lohmann, Christian Gierds and Dennis Reinert.


BPEL2oWFN is part of the Tools4BPEL project funded by the Bundesministerium für Bildung und Forschung. See http://www.informatik.hu-berlin.de/top/tools4bpel for details.

Table of Contents


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1 Overview

1.1 Introduction

BPEL2oWFN is a compiler translating a business processes expressed in BPEL (Business Process Execution Language for Web Services) [ACD^+03] into an oWFN (open Workflow Net) [MRS05]. This oWFN can be used to:

BPEL2oWFN uses static analysis to make the generated oWFN as compact as possible to analyze a chosen property. This is called flexible model generation (see Future Work).

BPEL2oWFN is the successor from BPEL2PN [SHS05], a Java-based compiler generating low-level Petri nets. BPEL2oWFN can be understood as a re-implementation for extensibility and performance issues. Its functionality is a superset of the functionality of BPEL2PN. 1

BPEL2oWFN was written by Niels Lohmann, Christian Gierds and Dennis Reinert. It is part of the Tools4BPEL project funded by the German Bundesministerium für Bildung und Forschung. See http://www.informatik.hu-berlin.de/top/tools4bpel for details.

1.2 Translation Process

The translation process of the BPEL business process is performed in six steps which we describe briefly in this section:

  1. Lexical and syntactical analysis. BPEL2oWFN parses the input process according to the specification of BPEL4WS version 1.1 [ACD^+03]. All information about the process is collected in a symbol table for further use.
  2. Semantic analysis. The input file is checked against the constraints of the specification, e.g. that each defined link has to be used as source and target exactly once. BPEL processes violating these constraints are rejected.
  3. AST generation. For further analysis steps the exact syntax (indentation etc.) is not used any more. The input process is represented as an AST (abstract syntax tree). While generating the AST, the implicit transformation rules of BPEL (e.g. the presence of an otherwise-branch with an empty activity) are applied.
  4. Net generation. The nodes of the AST are used to create the Petri net using the pattern database by applying `unparse'-rules (rules associating each node with a pattern).
  5. Net optimization (optional). To reduce the generated net several structural reduction rules can be applied, e.g. to merge sequences.
  6. Net output. The generated Petri net can be exported in several file formats.

1.3 Concepts of BPEL2oWFN

In this section we describe the main concepts of BPEL2oWFN used to realize the translation. Reading this section is not necessary for using BPEL2oWFN, yet knowing the underlying algorithms and data structures not only helps to locate bugs, but also helps you to customize BPEL2oWFN or request a feature.

1.3.1 Abstract Syntax Tree

The AST (abstract syntax tree) is an abstraction of the syntax tree generated while parsing the BPEL process: any unnecessary information (e.g. indention, brackets or other “syntax-supporting” elements) is omitted. It is the central data structure of BPEL2oWFN. The nodes of the AST are annotated with pointers to symbol table entries during the analysis steps. These annotations are used to select the most compact Petri net pattern from the pattern database to check a given property.

1.3.2 Pattern Repository

The idea of flexible model generation is to find the most compact model to check a given property. The patterns of the Petri net semantics of [Sta05] are designed to fit in any given context. However when the context is known some behavior modeled in the patterns (i.e. some of the nodes) can be safely removed without changing its semantics. BPEL2oWFN is designed to hold several sets of Petri net patterns each suitable in certain contexts. These patterns are collected in a pattern repository.

1.3.3 Petri Net Class

BPEL2oWFN provides many algorithms and data structures to build, represent, modify and simplify Petri nets and open workflow nets, resp. They are the interface between the pattern database and the file output for the model checking tool. The functions are collected in an extensible class allowing to add more output file formats, structural simplification rules (optimized to preserve certain properties such as deadlock freedom or liveness) or abstractions (e.g. abstraction from variables, abstraction from external behavior).

1.3.4 Control Flow Graph

Beside the dynamic analysis of the generated Petri net model with Fiona or classical model checking tools, BPEL2oWFN prototypically implements a control flow graph (CFG) (c.f. [Hei03]). This CFG can be used to check most of the constraints of the specification statically, i.e. without actually deploying and running the BPEL process. For example, the CFG can be used to check if each variable is initialized by an incoming message or an <assign> activity.


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2 Invoking BPEL2oWFN

The standard invocation of BPEL2oWFN is:

     bpel2owfn -i inputfile.bpel -f owfn -o

where inputfile.bpel is a BPEL process. The option -f owfn cause BPEL2oWFN to generate an open workflow net. This net is written to a file named inputfile.owfn, because of the option -o. For more examples, see Examples.

BPEL2oWFN can be called without any parameter. In this case, it acts as a simple parser for BPEL, that reads its input from the standard input (stdin).

2.1 Options

BPEL2oWFN supports the following command-line options:

Print an overview of the command-line options and exit.
Print version information and exit.
-i filename.bpel
Read BPEL input from file filename.bpel. If this parameter is omitted, input is read from standard input (stdin).
The generated files are written to a file called filename. If the short form is used or the filename is omitted, the input file name is taken and extended by the suffix of the chosen file format(s). If this parameter is omitted, the output is passed to the standard output (stdout).
All additional information like warnings and processing information are written to a file called filename. If the short form is used or the filename is omitted, the output file name is taken and extended by the suffix .log. If this parameter is omitted, the information is passed to the standard error output (stderr).
--debug=1-4 | flex | bison
-d 1-4 | flex | bison
This option triggers different debug levels, and can enable additional information from Flex and Bison about how the input is lexed and parsed.
This option makes BPEL2oWFN behave like its predecessor, BPEL2PN: it generates a Petri net LoLA format and an information file. The option --bpel2pn is a shortcut for --mode=petrinet --format=lola --format=info --output.

2.1.1 Modes

When invoking BPEL2oWFN several modes are possible.

-m modus
BPEL2oWFN supports four different modes for handling BPEL, so modus can be one of the following options:
Outputs the AST (abstract syntax tree) generated while parsing the input file to standard output. This option is mostly used for debugging reasons since it shows the implicit transformations and the phylum names used when generating the Petri net.
For control flow analysis (a form of static analysis) a CFG (Control Flow Graph) is generated. It can be printed in graphical (dot) representation. This option is in an early beta-stage and can only check for uninitialzed variables yet. For more information, see Future Work.
Generates a Petri net representing the semantics of the given process. Other options can be added to simplify or modify that generated Petri net (see below).
Outputs the parsed BPEL file in XML representation. Any unnecessary attributes are omitted. This option is mostly used for debugging reasons as it shows the implicit transformations and the identifiers of the BPEL constructs.
Please note that you can only use at most one mode.

2.1.2 Additional parameters

These options control some Petri net-related options. See Petri Net-related Functions for more details.

-p par
When the parameter is set, the pattern for the message event handler is cyclic as depicted in Fig. 30/31 of [Sta05]. If the parameter is not set (standard case), the pattern is acyclic: the activity embedded in the event handler is executed at most once, depended on the incoming messages.
When the parameter is set, the pattern for the <while> activity is cyclic as depicted in Fig. 18 of [Sta05]. If the parameter is not set (standard case), the pattern is acyclic: the activity embedded in the <while> activity is at most executed once, chosen non-deterministically.
Add an extra loop transition to the final place of the generated Petri net to live-lock the system in order to find deadlocks.
With this parameter, standard faults may not occure in activities directly nested in a fault handler.
When the parameter is set, only used-defined faults using the <throw> activity can occur.
Removes places of the generated Petri net modelling variables as well as the place modelling the system clock.
Structurally simplify the generated Petri net.

If you want to enable more than one parameter you have to add -p/ --parameter to each parameter.

2.1.3 Output formats

Especially for the Petri net mode, a variaty of output formats are supported, see File Formats for more information. There are invoked by the following option:

-f fileformat
Create a Petri net in APNN (Abstract Petri Net Notation). Implies the mode petrinet.
Create a dot representation of the structure generated in the current mode which can be any kind of Petri net (mode petrinet or the control flow graph (mode cfg).
Create an additional information file. Implies the mode petrinet.
Create a LoLA place/transition net. Implies the mode petrinet.
Create a low-level oWFN in Fiona file format. Implies the mode petrinet.
Create a Petri net in low-level PEP notation. Implies the mode petrinet.
Create a PNML Petri net. Implies the mode petrinet.
Create an XML (Extensible Markup Lanuage) file. Implies the mode pretty.

If you want to use more than one output file format you have to add -f/ --fileformat to each file format. Please note that the underlying modes of the given file formats are the same, i.e. you cannot create XML and LoLA files together since XML uses the mode pretty whereas LoLA uses the mode petrinet.

2.2 Examples

In this section we show some examples how BPEL2oWFN can be invoked.

bpel2owfn -i sample.bpel -flola -finfo -o -p simplify
Reads the file sample.bpel, generates a structural simplified low-level Petri net and saves it in a LoLA file sample.lola. For further information a file sample.info is generated.
bpel2owfn -i sample.bpel -fowfn -d3 -o
Reads the file sample.bpel, generates a low-level open workflow net and saves it in an oWFN file sample.owfn. For further information a file sample.info is generated. During the conversion several debug messages are printed to standard output.
prog | bpel2owfn -fdot -m petrinet | dot -Tpng -osample.png
Runs the program prog and reads its output as BPEL process, generates a Petri net and outputs its Dot representation. This stream is read by Dot which layouts the Petri net and creates an output PNG (Portable Network Graphic) file sample.png.
bpel2owfn -i sample.bpel -m ast
Reads the file sample.bpel and prints the abstract syntax tree (AST) to standard output.

2.3 Exit Values

When BPEL2oWFN is invoked and run without any error, the exit value is 0.

No error. The input file could be correctly opened, parsed and the output file(s) could be generated without any error.
Lexical or syntax error. This error occurs while lexing or parsing the input file. It is thrown by the lexer or the parser, resp. Usually the `source' of the error (i.e. the filename and line number) is indicated together with the unexpected (last read) and expected token.

An example:

          Error while parsing
          syntax error, unexpected X_SLASH, expecting X_OPEN
          Error in `example.bpel' in line 12:
            token/text last read was `/'

Please note that the indicated position (i.e. the line number) may be fuzzy — it should be understood as a hint to the erroneous line.

`File not found' exception. The given input file was not found resp. could not be opened.

An example:

          An error has occurred while parsing "example.bpel"!
          Exception #2 occurred!
             File `example.bpel' not found.

`File could not be opened' exception. An output file could not be opened for write access. You may check the appropriate for the target directory or the file if it already exists.

An example:

          An error has occured while parsing "example.bpel"!
          Exception #3 occured!
             File "example.dot" could not be opened for writing access!

Option mismatch. The given command-line options cannot be processed together.

An example:

          An error has occurred while parsing "example.bpel"!
          An error has occured while parsing "<STDIN>"!
          Exception #10 occured!
             Choose only one mode
           Additional information:
             Type ./bpel2owfn -h for more information.

`Dynamic cast error' exception. While building an internal scope tree an unexpected error has occurred.
Node not found.
`Node already defined' exception. While generating the Petri net a node was found having a history entry covered by another node before.

An example:

          An error has occurred while parsing "example.bpel"!
          Exception #41 occurred!
             Place with role `1.internal.final' already defined.

`Merging error' exception. While generating the Petri net an error occurred while merging two nodes. It happens either when one of the nodes was not found or one of the nodes is a guarded transition—the merging of guarded transitions is not yet supported.
`Arc error' exception. While generating the Petri net an error occurred while adding an arc to the net. It happens either on type errors — i.e. an arc between two transitions (or two places, resp.) should be drawn — or when the source or target node of an arc was not found.

Please report the occurrence of any exception with numbers 30–50 since it indicates a bug in BPEL2oWFN we would like to fix immediately (see Reporting Bugs).


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3 File Formats

BPEL2oWFN can generate several file formats:

3.1 Petri Net File Formats

These file formats output the generated Petri net model to various Petri net file formats to support as much model checking and analysis tools as possible. The nodes of the Petri net are named using the internal (numeric) names generated by BPEL2oWFN. For more information on the node naming conventions of BPEL2oWFN, see Naming Conventions.

In all file formats, the inital place of the process, the process clock and all variable places are initially marked.

LoLA place/transition net
A (low-level) place/transition net as described in [LoLA]. The first entry of the history of each node is added as a comment.
oWFN in Fiona format
An open workflow net is a Petri net with an interface, i.e. two sets of places: input places and output places. Additionally an open workflow net has a set of final markings. To represent oWFNs the LoLA format was extended to implement this categorization.
Petri Net Markup Language (PNML)
A (low-level) place/transition net in Petri Net Markup Language as described in [WK02]. An arcname value is just added to meet the syntactic requirements and is just an enumeration of the arcs (a1, a2, ...).
Abstract Petri Net Notation (APNN)
A (low-level) place/transition net in Abstract Petri Net Notation as described in [BKK95]. An arcname value is just added to meet the syntactic requirements and is just an enumeration of the arcs (a1, a2, ...).
Low-level PEP Notation
A (low-level) place/transition net in low-level PEP (Programming Environment based on Petri Nets) notation as described in [PEP].

3.2 Info-files

The Info-files are generated when any command-line option is used which imply Petri net-generation. When reading from a file process.bpel a file process.info is generated. This file sums up all places and transitions together with their internal (numeric) name and their complete history:

     ID  TYPE        ROLES
     a list of places
     ID      ROLES
     a list of transitions

These files are generated to document the connection between the generated output file and the chosen Petri net patterns. In future distributions of BPEL2oWFN the Info-files will be used to annotate witness and counter-example paths, resp. and to “re-translate” Petri net properties (e.g. a dead transition) to the input BPEL process.

3.2.1 Naming Conventions

BPEL2oWFN generates the output Petri net by creating and merging parameterized patterns of the Petri net semantics defined in [Sta05]. Due to merging and simplifying the Petri net nodes “belong” to more than one pattern. For example, in a sequence the initial place of the sequence and the initial place of its first activity are merged so that the final Petri net contains one place with two roles.

The roles of each place are collected during the Petri net generation. They form the history of the node. It is used to locate errors of the modeled business process: If, for example, BPEL2oWFN generates a Petri net of a business process and the model checker LoLA finds a dead transition, its history helps to find which BPEL constructs are affected and in this case will never be executed.

The roles are named using the following conventions:

3.3 Dot Graphics

To bugfix2 the implemented Petri net patterns BPEL2oWFN implements a graph representation of the generate Petri net. Furthermore, the CFG can be printed as dot output.


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4 Petri Net Patterns

In version 1.2 of BPEL2oWFN the following Petri net patterns are implemented:

4.1 Petri net semantics from [Sta05]

The Petri net semantics for BPEL4WS from Christian Stahl (Humboldt-Universität zu Berlin) published in [Sta05].

4.1.1 Overview

Feature complete semantics covering both positive control flow with event handling and negative control flow (fault and compensation handling).

4.1.2 Limitations of the semantics

4.1.3 Changes and Modulation

We tried to stick as close to the Petri net patterns of [Sta05] as possible. However, the implemented patterns in the pattern database sometimes differ to the given patterns due to discovery of bugs or implementation decisions. In this subsection we sum up these changes to help you understand the generated Petri net model.


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5 Petri Net-related Functions

Currently implemented Petri net-specific functions:

5.1 Structural Simplification

These structural reduction rules are implemented in the command-line option --parameter=simplify, see Invoking BPEL2oWFN). To acheive a better reduction, combine the parameter with --parameter=novarialbles.

5.2 Abstractions

5.3 Markings

The following places are initially marked to ensure a deadlock-free model of processes with “reasonable” control-flow (e.g. with an acyclic link structure):


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6 Limitations and Bugs

6.1 Known Bugs

As this is the first public version of BPEL2oWFN the translation from a BPEL process to an open workflow net might be unstable or incorrect in some few scenarios:

6.2 Reporting Bugs

If you find a bug in BPEL2oWFN, please first check that it is not a known bug listed in `Known Bugs'. Otherwise please send us an electronic mail to nlohmann@informatik.hu-berlin.de. Include the version number which you can find by running bpel2owfn --version. Also include in your message the input BPEL process and the output that the program produced. We will try to answer your mail within a week.

If you have other questions, comments or suggestions about BPEL2oWFN, contact us via electronic mail to nlohmann@informatik.hu-berlin.de.

6.3 Contact Person

Niels Lohmann

Humboldt-Universität zu Berlin
Institut für Informatik
Unter den Linden 6
10099 Berlin, Germany

(+49) (30) 2093-3070
(+49) (30) 2093-3067


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7 Future Work

For future releases of BPEL2oWFN the following features are planned:


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Appendix A References

Tony Andrews, Francisco Curbera, Hitesh Dholakia, Yaron Goland, Johannes Klein, Frank Leymann, Kevin Liu, Dieter Roller, Doug Smith, Satish Thatte, Ivana Trickovic, and Sanjiva Weerawarana. Business Process Execution Language for Web Services, Version 1.1. Technical report, BEA Systems, IBM, Microsoft, SAP, Siebel Systems. May 2003.
Falko Bause, Peter Kemper, and Pieter Kritzinger. Abstract Petri Net Notation. Petri Net Newsletter 49:9-27, October 1995. 3
Peter Massuthe and Daniela Weinberg. Fiona.4
Thomas Heidinger. Statische Analyse von BPEL4WS-Prozessmodellen (in German). Studienarbeit, Humboldt-Universität zu Berlin, December 2003. 5
Karsten Schmidt. LoLA: A Low Level Analyser. Manual. 6
Axel Martens. Verteilte Geschäftsprozesse – Modellierung und Verifikation mit Hilfe von Web Services (in German). PhD thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2003.
Javier Esparza, Claus Schröter, and Stefan Schwoon. Model-Checking Kit. 7
Peter Massuthe, Wolfgang Reisig, and Karsten Schmidt. An Operating Guideline Approach to the SOA. Proceedings of the 2nd South-East European Workshop on Formal Methods 2005 (SEEFM05), Ohrid, Republic of Macedonia, 2005. 8
University of Oldenburg, Department of Computing Science. PEP (Programming Environment based on Petri Nets). Manual. 9
Karsten Schmidt. LoLA: A Low Level Analyser. In: Mogens Nielsen, and Dan Simpson, editors: Application and Theory of Petri Nets, 21st International Conference (ICATPN 2000), pp. 465-474, Springer-Verlag (LNCS 1825), June 2000.
Sebastian Hinz, Karsten Schmidt, and Christian Stahl. Transforming BPEL to Petri Nets. In W.M.P. van der Aalst, B. Benatallah, F. Casati, and F. Curbera, editors, Proceedings of the Third International Conference on Business Process Management (BPM 2005), pp. 220-235, Springer-Verlag (LNCS 3649), September 2005. 10
Christian Stahl. A Petri Net Semantics for BPEL. Informatik-Berichte 188, Humboldt-Universität zu Berlin, July 2005. 11
Daniela Weinberg. Analyse der Bedienbarkeit. Diplomarbeit, Humboldt-Universität zu Berlin, October 2004. 12
Michael Weber and Ekkart Kindler. The Petri Net Markup Language. In: Hartmut Ehrig, Wolfgang Reisig, Grzegorz Rozenberg, Herbert Weber, editors: Petri Net Technology for Communication-Based Systems: Advances in Petri Nets, pp. 124-144, Springer Verlag (LNCS 2472), January 2003.13


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Appendix B GNU General Public License

Version 2, June 1991
     Copyright © 1989, 1991 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.


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When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

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We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

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How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.

     one line to give the program's name and an idea of what it does.
     Copyright (C) 19yy  name of author
     This program is free software; you can redistribute it and/or
     modify it under the terms of the GNU General Public License
     as published by the Free Software Foundation; either version 2
     of the License, or (at your option) any later version.
     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     GNU General Public License for more details.
     You should have received a copy of the GNU General Public License along
     with this program; if not, write to the Free Software Foundation, Inc.,
     59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) 20yy name of author
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
     type `show w'.  This is free software, and you are welcome
     to redistribute it under certain conditions; type `show c'
     for details.

The hypothetical commands show w and show c should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than show w and show c; they could even be mouse-clicks or menu items—whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright
     interest in the program `Gnomovision'
     (which makes passes at compilers) written
     by James Hacker.
     signature of Ty Coon, 1 April 1989
     Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.


[1] In fact, BPEL2oWFN can simulate the behavior of BPEL2PN with a command-line parameter (see Invoking BPEL2oWFN).

[2] The Petri nets usually have a large number of nodes so that the graphical representation of a `real world' process would not be suitable to process, read or understand. That is why the Dot output shall be seen as a means to debug small patterns.

[3] http://ls4-www.informatik.uni-dortmund.de/QM/MA/fb/publication_ps_files/APNN.ps.gz

[4] Soon available at http://www.informatik.hu-berlin.de/top/tools4bpel/fiona

[5] http://www.informatik.hu-berlin.de/top/download/publications/heidinger03.pdf

[6] http://www.informatik.hu-berlin.de/top/lola/doku.ps

[7] http://www.fmi.uni-stuttgart.de/szs/tools/mckit

[8] http://www.informatik.hu-berlin.de/top/download/publications/MassutheReisigSchmidt-OGApproach.ps

[9] http://parsys.informatik.uni-oldenburg.de/~pep

[10] http://www.informatik.hu-berlin.de/top/bpel2pn

[11] http://www.informatik.hu-berlin.de/Institut/struktur/systemanalyse/preprint/stahl188.pdf

[12] http://www.informatik.hu-berlin.de/top/download/publications/weinberg04.pdf

[13] http://www.informatik.hu-berlin.de/top/pnml/download/about/PNML_LNCS.pdf