About this document:
This manual is for BPEL2oWFN, Version 1.0, a tool translating business processes described in BPEL to open workflow nets (oWFN), last updated 16 January 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.
BPEL2oWFN is a compiler translating a business processes expressed in BPEL (Business Process Execution Language for Web Services) [ACD^+03] to an oWFN (open Workflow Net) [MRS05]. This oWFN can be used to:
In future versions of BPEL2oWFN static analysis is used to find the smallest oWFN to analyze a chosen property. This is called flexible model generation (see Future Work).
BPEL2oWFN was written by Niels Lohmann, Christian Gierds and Dennis Reinert. It 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.
The translation process of the BPEL business process is performed in six steps which we describe briefly in this section:
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.
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 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.
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 database.
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 (e.g. PNML (Petri Net Markup Language), PEP notation, etc.), 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).
The standard invocation of BPEL2oWFN is:
bpel2owfn -f inputfile.bpel -O2F
where inputfile.bpel is a BPEL process. The option
-O2F causes BPEL2oWFN to generate an open workflow
net named inputfile.owfn and a file inputfile.info
describing the places and transitions of the net. For more examples,
see Examples.
BPEL2oWFN supports the following command-line options:
When invoking BPEL2oWFN several output modes are possible. While the -pn-mode can be implied by other options the other modes have to be set explicitly. Either way, at most one of these options can be chosen.
These options imply the -pn-option. When BPEL2oWFN is run with the -pn-option reading a file input.bpel, a file input.info holding the information about the nodes of the created Petri net is generated. See Naming Conventions for more information.
In this section we show some examples how BPEL2oWFN can be invoked.
When BPEL2oWFN is invoked and run without any error, the exit value is 0.
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.
An example:
An error has occurred while parsing "example.bpel"!
Exception #2 occurred!
File `example.bpel' not found.
|
An example:
An error has occurred while parsing "example.bpel"!
Exception #10 occurred!
Chosen parameters cannot work together (see parameter -h).
Additional information:
LoLA and dot output on stdout are confusing, chose one!
|
An example:
An error has occurred while parsing "example.bpel"!
Exception #41 occurred!
Place with role `1.internal.final' already defined.
|
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).
BPEL2oWFN can generate several file formats:
A (low-level) place/transition net as described in [LoLA]. The places and transitions are named using the internal (numeric) name of each node. Furthermore, the first entry of the history of each node is added as a comment.
{ Petri net created by BPEL2oWFN reading filename.bpel }
PLACE
a comma-separated list of places
MARKING
the initial marking
a comma-separated list of transitions
{ END OF FILE }
|
For more information on the node naming conventions of BPEL2oWFN, see Naming Conventions.
An open workflow net is a Petri net with an interface, i.e. two sets of places: input places and output places. To represent oWFNs the LoLA format was extended to implement this categorization:
{ oWFN created by BPEL2oWFN reading filename.bpel }
PLACE
INPUT
a comma-separated list of input places
OUTPUT
a comma-separated list of output places
INTERNAL
a comma-separated list of internal places
MARKING
the initial marking
a comma-separated list of transitions
{ END OF FILE }
|
Additionally an open workflow net has a set of final markings. Since there exist no tools reading oWFNs yet, the representation of final markings is not implemented.
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:
PLACES:
ID TYPE ROLES
a list of places
TRANSITIONS:
ID GUARD 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.
For more information on the node naming conventions of BPEL2oWFN, see 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:
For example, BPEL's activity process has the identifier 1, so that all nodes of the process pattern begin with 1.. To find out the identifiers of a given process use the --xml command-line option which prints the id of each activity as an XML attribute.
The same schema is used for fault handlers (id.internal.faultHandler.), compensation handlers (id.internal.compensationHandler.) and event handlers (id.internal.eventHandler.), resp.
To bugfix1 the implemented Petri net patterns BPEL2oWFN implements a graph representation of the generate Petri net.
In version 1.0 of BPEL2oWFN the following Petri net patterns are implemented:
The Petri net semantics for BPEL4WS from Christian Stahl (Humboldt-Universität zu Berlin) published in [Sta04].
Feature complete semantics covering both positive control flow with event handling and negative control flow (fault and compensation handling).
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.
Furthermore, all failed places of the activities were removed. In the original Petri net semantics, all faults of a scope were collected on the fault_in of the stop-pattern and then classified as being the first fault of the scope, a following fault, a fault from the fault handler, a fault from the compensation handler, or a fault from a child scope. In our implementation, new places (fh_fault_in and ch_fault_in) were introduced and each activity throws its faults to the “correct” place automatically.
To ensure that at most one error can occur (i.e. at most one token is produced on any fault place) the fault places are guarded by state places: To throw a fault from an activity enclosed in a scope, the state of that scope has to be Active. The first thrown fault changes the state to !Active thus preventing more faults to occur. The places fh_fault_in and ch_fault_in, resp. are guarded by !FHFaulted/FHFaulted and !CHFaulted/CHFaulted, resp.
Moreover, the generated Petri nets have less nodes than those generated by BPEL2PN [SHS05] since an unfolding of the reset arcs in not necessary any more.
Beside performance (e.g. only 1 bit is needed to store the marking of a place) and compatibility issues (e.g. 1-safety is a prerequisite to use the Model Checking Kit [MCK]), features not supported by the Petri net semantics can be discovered since the generated net will most likely violate 1-safety when an unsupported BPEL feature is used. If, for example, a scope is enclosed in a while loop (which would model instantiation which is not supported by the Petri net semantics Limitations of the semantics), the state places of that scope would not be 1-safe.
The assign activities are sufficiently short-lived that they are allowed to complete rather than being interrupted when termination is forced.
This change fixes a bug in the Petri net semantics.
In future versions of BPEL2oWFN these found deadlocks shall be mapped back into the BPEL code to highlight the “unreasonable” activities (i.e. a cycle-closing link).
Currently implemented Petri net-specific functions:
These structural reduction rules are implemented in the command-line option --simplify, see Invoking BPEL2oWFN).
These abstractions are implemented in the command-line option --low-level.
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):
All interleavings should end in a livelock-marking which covers 1.internal.final and in which only transition 1.internal.finishloop can fire. All livelock-markings differ in the marking of the state places of the process and its child scopes.
Deadlocks indicate modeling mistakes (e.g. a cyclic link structure). Non-1-safe markings indicate the usage of an unsupported feature of the Petri net semantics (e.g. instantiation, see Limitations of the semantics).
The current version of BPEL2oWFN underlies several limitations:
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:
Solution: Each communicating activity (i.e. invoke,
receive, reply) should be defined with (input/output)
variables.
Solution: Avoid using the -s mode in this case.
bpws'. Processes using these elements are rejected with a
syntax error message.
Solution: Try removing or commenting these elements.
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.
Niels Lohmann
Humboldt-Universität zu Berlin
Institut für Informatik
Unter den Linden 6
10099 Berlin, Germany
For future releases of BPEL2oWFN the following features are planned:
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[1] 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.
[2] Tool available at http://www.informatik.hu-berlin.de/top/bpel2pn
[3] http://www.informatik.hu-berlin.de/top/lola/doku.ps
[4] http://www.fmi.uni-stuttgart.de/szs/tools/mckit
[5] http://www.informatik.hu-berlin.de/top/download/publications/MassutheReisigSchmidt-OGApproach.ps
[6] http://www.informatik.hu-berlin.de/Institut/struktur/systemanalyse/preprint/stahl188.pdf
[7] http://www.informatik.hu-berlin.de/top/download/publications/weinberg04.pdf