GNU BPEL2oWFN User's Manual


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GNU BPEL2oWFN

About this document:

This manual is for GNU BPEL2oWFN, version 2.0.2, a tool translating a BPEL process into an open workflow net (oWFN), last updated 15 June 2007.

Copyright © 2005, 2006, 2007 Niels Lohmann

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.”

(a) The FSF's Back-Cover Text is: “You have freedom to copy and modify this GNU Manual, like GNU software.”

This manual does not explain how to setup or install GNU BPEL2oWFN. For this information please read the Installation Manual which is part of the distribution, or can be downloaded from the website of GNU BPEL2oWFN, http://www.gnu.org/software/bpel2owfn.
images/tools4bpel.png
GNU BPEL2oWFN was developed during the Tools4BPEL project funded by the German Federal Ministry for Education and Research (BMBF), see http://www.informatik.hu-berlin.de/top/tools4bpel for details.

Table of Contents


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1 Introducing BPEL2oWFN

BPEL2oWFN translates a web service expressed in WS-BPEL (Web Service Business Process Execution Language) into an oWFN (open Workflow Net). This oWFN can be used to:


images/diagram.png


Furthermore, BPEL2oWFN can translate a BPEL4Chor choreography to a Petri net model. This model can be used to analyze properties of a complete choreography or to synthesize a fitting service for an incomplete choreography.

BPEL2oWFN uses static analysis to make the generated Petri net model as compact as possible to analyze a chosen property. This is called flexible model generation. Furthermore, several design flaws can be detected using control and data flow analysis.

BPEL2oWFN was written by Niels Lohmann, Christian Gierds and Martin Znamirowski. 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.

1.1 Concepts of BPEL2oWFN

Input BPEL Process BPEL2oWFN can read BPEL processes compliant to the WS-BPEL 2.0 or the BPEL4WS 1.1 specification.


Abstract Syntax Tree The AST (abstract syntax tree) is the main data structure of BPEL2oWFN. The AST is annotated with information gained by static analysis.


Control/Data Flow Graph From the abstract syntax tree, a control/data flow graph is built. This graph is used to apply static analysis algorithms to gain information (e.g., dead code) about the process. These algorithms Furthermore, design flaws such as cyclic control links or conflicting receiving activities are detected.


Petri Net API The annotated abstract syntax tree is used to generate a Petri net model of the BPEL process. All Petri net-related functions (adding, removing and merging of nodes; structural reduction) are provided by the Petri net API (application programming interface).


Pattern Repository For each BPEL construct, several patterns with different degrees of abstraction are stored in the pattern repository. Using the information gained by static analysis, the most abstract pattern applicable is used.


Output Petri Net The generated Petri net model can be exported to many file formats, such as PNML, LoLA, Fiona oWFN, INA, APNN, or PEP.


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2 Invoking BPEL2oWFN

The standard invocation of BPEL2oWFN is:

     bpel2owfn -i service.bpel -m petrinet -f owfn -o

where service.bpel is a BPEL process. The option -f owfn causes BPEL2oWFN to generate an open workflow net (option -m petrinet). This net is written to a file named service.owfn, because of the option -o.

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

2.1 Options

BPEL2oWFN supports the following command-line options:

--help
-h
Print an overview of the command-line options and exit.
--version
-v
Print version information and exit.
--input=filename.bpel
-i filename.bpel
Read a BPEL process from file filename.bpel. If this parameter is omitted, input is read from standard input (stdin). Wildcards such as process*.bpel are also allowed.
--wsdl=filename.wsdl
-w filename.wsdl
Read a WSDL file to support the translation.
--topology=filename.xml
-t filename.xml
Read a BPEL4Chor participant topology file to support the translation of BPEL4Chor choreographies. Can only be used with the choreography mode.
--output[=filename]
-o
The generated output is 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).
--log[=filename]
-l
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.

Debug level:

0
When errors are found, only display the error code and skip additional information.
1
No debug information, but display warning and error messages. Furthermore, detailled information about syntax errors are displayed.
2
All messages from -d1. Additionally, information about the current steps is displayed.
3
All messages from -d2. Additionally, the structure of the process is shown, i.e. when a Petri net is generated...
4
All messages from -d3. Additionally, a message is displayed each time a function is entered or left.
flex
Displays messages from Flex. Can be combined with any other debug level.
bison
Displays messages from Bison. Can be combined with any other debug level.

--reduce=0-5
-r 0-5
Apply several structural reduction rules to the generated Petri net model (implies mode petrinet or choreography). The rules preserve deadlocks, livelocks and all deadlock-free communicating partners. The rules are organized in reduction levels:
0
No rules are applied (standard).
1
Structural dead nodes are removed; that is, unmarked places with empty preset and transitions with a dead place in its preset are removed.
2
All reduction rules from -r1. Additionally, unnecessary status places are removed. A status place is considered unnecessary if it has no outgoing arcs.
3
All reduction rules from -r2. Additionally, identical nodes are merged. Two nodes are considered identical if their presets and postsets are equal:
images/rb1.png images/rb2.png
4
All reduction rules from -r3. Additionally, remove serial nodes:
images/ra1.png images/ra2.png
5
All reduction rules from -r4. Additionally, remove self-loop nodes.

2.1.1 Modes

When invoking BPEL2oWFN several modes are possible.

--mode=modus
-m modus
BPEL2oWFN supports different modes for handling input BPEL files: modus can be one of the following:
ast
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.
cfg
For control flow analysis (a form of static analysis) a CFG (Control Flow Graph) is generated. It can be printed in graphical (dot) representation. With the CFG, several design flaws of BPEL processes such as cyclic control links or read access to uninitialized variables can be detected statically. Furthermore, faulty constellations such as conflicting receiving activities can be found using the cfg mode.
choreography
The choreography mode2 is an extension of the petrinet mode. In the choreography mode, several BPEL processes can be parsed, and a Petri net model of their composition is generated.

For examples, check test/bpel4chor directory. When combined with LoLA file output, an additional .task file is generated. With the help of this file LoLA can check for weak termination of the composition.

Note that the choreography mode is only tested with the small mode. To support the translation of a BPEL4Chor choreography, a participant topology can be additionally parsed using the topology parameter.

petrinet
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).
pretty
Outputs the parsed BPEL file in XML representation. This option is mostly used for debugging reasons as it shows the implicit transformations and the identifiers of the BPEL constructs.

At most one mode can be selected. If no mode is given, BPEL2oWFN acts like a plain BPEL parser; that is, the input file is read, but no output is generated.

2.1.2 Additional parameters

These options control some Petri net-related options.

--parameter=par
-p par
small
With the small parameter3, only the communicational behavior of the input BPEL process is modeled. That is, the negative control flow (fault, termination, or compensation handlers, as well as <exit>, <throw>, <compensate>, <compensateScope> activities) is not translated to the Petri net model. When combined with reduce, this parameter yields the most compact Petri net model.
fhfaults
Confines the standardfaults parameter: in the negative control flow (in activities in fault handlers), no further BPEL standard faults can occur.
nointerface
When creating a .dot file, no interface is printed.
reduce
Apply all implemented structural reduction rules. This parameter is a shortcut for -r5 and overrides any other defined reduction level.
standardfaults
Model the occurrence of standard faults. When this parameter is ommited, only user-defined faults, that is, faults thrown with <throw> activities, and join failures can occur. With the standardfaults parameter, also the occurrence of other BPEL standard faults is modeled. This parameter yields the most-detailled, and thus biggest Petri net model.
variables
Add places for the variables of the input BPEL process to the Petri net model. As the generated model abstracts from data, that is, a low-level Petri net is generated, the variables parameter also does not introduce data aspects. Thus, this mode is experimental.

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. There are invoked by the following option:

--format=fileformat
-f fileformat
Creates a file in a given ouput file format. Each file format is only available in certain modes. If you want to use more than one output file format you have to add -f/ --format to each file format. Please note that the underlying modes of the given file formats are the same. You cannot, for example, create XML and LoLA files together since XML requires the mode pretty, whereas LoLA requires the mode petrinet.
Petri net file formats (imply mode petrinet or choreography):
apnn
Outputs the inner of the generated open workflow net in APNN (Abstract Petri Net Notation). When the parameter -o is used, a file with the suffix .apnn is created.
ina
Outputs the inner of the generated open workflow net as untimed low-level Petri net in INA (Integrated Net Analyzer) format. When the parameter -o is used, a file with the suffix .pnt is created.
lola
Outputs the inner of the generated open workflow net as low-level Petri net in LoLA (Low-Level Analyzer) file format. When the parameter -o is used, a file with the suffix .lola is created.
owfn
Outputs the generated open workflow net in Fiona file format. Note that the Fiona file format is — together with the PNML file format — the only Petri net output format that outputs the complete open workflow net, that is, also the interface is exported. When the parameter -o is used, a file with the suffix .owfn is created.
pep
Outputs the inner of the generated open workflow net as low-level Petri net in low-level PEP notation. When the parameter -o is used, a file with the suffix .llnet is created.
pnml
Outputs the generated open workflow net in PNML (Petri Net Markup Language). Note that the PNML file format is — together with the Fiona file format — the only Petri net output format that outputs the complete open workflow net, that is, also the interface is exported. Currently, the interface places are annotated using a <type> tag which is only supported by Yasper4. When the parameter -o is used, a file with the suffix .pnml is created.
spin
Outputs the inner of the generated open workflow net as low-level Petri net in Promela (Process Meta Language) for the model checker SPIN. When the parameter -o is used, a file with the suffix .spin is created.

Other file formats (note the required mode):
dot
When mode petrinet is used, the generated open workflow net is printed in Graphviz dot representation. When mode ast is used, the AST (abstract syntax tree) is printed in Graphviz dot representation. When mode cfg is used, the CFG (control flow graph) is printed in Graphviz dot representation.

In any case, when the tool dot is found in the search path during configuration of BPEL2oWFN and the parameter -o is used, dot is used to generate a PNG (Portable Network Image) file. In this case, two files with the suffixes .dot and .png are created. Note that when the ast mode is used with the dot file format, the -o parameter has to be used.

info
When mode petrinet is used, information about the places and transitions of the generated net in a proprietary ASCII-based format. For each place and transition, all roles, that is, inscriptions of the Petri net patterns, are listed. The information can be used to correlate the generated Petri net model with the input BPEL process. When the parameter -o is used, a file with the suffix .info is created.
xml
When the mode pretty is used, the pretty-printed input BPEL process — with the implicit transformation rules applied – exported in XML (Extensible Markup Lanuage). When the parameter -o is used, a file with the suffix .xml is created.

2.2 Exit Values

0
No error occurred.
1
A critical error occured; that is, a fault was detected that makes further processing impossible.
2
An input file could not be opened.
3
A syntax error in the input BPEL occurred. The input file cannot be further processed.
4
Any other error.

2.3 Examples

In this section we show some examples how BPEL2oWFN can be invoked. See File Formats for more examples.

bpel2owfn -i sample.bpel -m petrinet -f lola -f info -o -p reduce
Reads the file sample.bpel, generates a structural reduced 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 -mpetrinet -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 -Tps -osample.ps
Runs the program prog and reads its output as BPEL process, generates a Petri net and outputs its Graphviz dot representation. This stream is read by dot which layouts the Petri net and creates an output PostScript file sample.ps.
bpel2owfn -i sample.bpel -m ast
Reads the file sample.bpel and prints the abstract syntax tree (AST) to standard output.
bpel2owfn -m choreography -i service1.bpel -i service2.bpel -f lola -o
Reads the files service1.bpel and service2.bpel and creates a Petri net model of their composition. The result is written to the LoLA file service1_service2.lola. Furthermore, an analysis file service1_service2.task is written that can be processed by LoLA.

Further examples for invocations of BPEL2oWFN can be found in the tests directory of the source distribution.


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3 Warnings and Error Messages

BPEL2oWFN performs several analysis steps on the input BPEL process. These messages are displayed during parsing and postprocessing of the process, and can be classified as follows:

An example for a message is this:

     CubeManagement.bpel:566 - [W00114]
     variable `waitResponse' used as `variable' in <from> might be uninitialized

The first line contains the filename of the input process CubeManagement.bpel and the line number 566 of the displayed issue. The line number might be imprecise; that is, it might deviate up or down a few lines. After the line number, the error code is displayed. W00114 stands for a warning with code 114. The detailed description of the messages can be suppressed with option -d0.

Further details can be taken from the table below.

Code Type Description


2 static analysis A WS-BPEL processor MUST reject any WSDL portType definition that includes overloaded operation names.5


3 static analysis If the value of exitOnStandardFault of a <scope> or <process> is set to "yes", then a fault handler that explicitly targets the WS-BPEL standard faults MUST NOT be used in that scope.


6 static analysis The <rethrow> activity MUST only be used within a faultHandler (i.e. <catch> and <catchAll> elements).


5 static analysis If the portType attribute is included for readability, in a <receive>, <reply>, <invoke>, <onEvent> or <onMessage> element, the value of the portType attribute MUST match the portType value implied by the combination of the specified partnerLink and the role implicitly specified by the activity.


7 static analysis The <compensateScope> activity MUST only be used from within a faultHandler, another compensationHandler, or a terminationHandler.


8 static analysis The <compensate> activity MUST only be used from within a faultHandler, another compensationHandler, or a terminationHandler.


15 static analysis To be instantiated, an executable business process MUST contain at least one <receive> or <pick> activity annotated with a createInstance="yes" attribute.


16 static analysis A partnerLink MUST specify the myRole or the partnerRole, or both.


17 static analysis The initializePartnerRole attribute MUST NOT be used on a partnerLink that does not have a partner role.


18 static analysis The name of a partnerLink MUST be unique among the names of all partnerLinks defined within the same immediately enclosing scope.


23 static analysis The name of a variable MUST be unique among the names of all variables defined within the same immediately enclosing scope.


24 static analysis Variable names are BPELVariableNames, that is, NCNames (as defined in XML Schema specification) but in addition they MUST NOT contain the . character.


25 static analysis The messageType, type or element attributes are used to specify the type of a variable. Exactly one of these attributes MUST be used.


32 static analysis For <assign>, the <from> and <to> element MUST be one of the specified variants.6


35 static analysis In the from-spec of the partnerLink variant of <assign> the value "myRole" for attribute endpointReference is only permitted when the partnerLink specifies the attribute myRole.


36 static analysis In the from-spec of the partnerLink variant of <assign> the value "partnerRole" for attribute endpointReference is only permitted when the partnerLink specifies the attribute partnerRole.


37 static analysis In the to-spec of the partnerLink variant of <assign> only partnerLinks are permitted which specify the attribute partnerRole.


44 static analysis The name of a <correlationSet> MUST be unique among the names of all <correlationSet> defined within the same immediately enclosing scope.


51 static analysis The inputVariable attribute MUST NOT be used on an Invoke activity that contains <toPart> elements.


52 static analysis The outputVariable attribute MUST NOT be used on an Invoke activity that contains <toPart> elements.


55 static analysis For <receive>, if <fromPart> elements are used on a <receive> activity then the variable attribute MUST NOT be used on the same activity.


56 static analysis A “start activity” is a <receive> or <pick> activity that is annotated with a createInstance="yes" attribute. Activities other than the following: start activities, <scope>, <flow> and <sequence> MUST NOT be performed prior to or simultaneously with start activities.


57 static analysis If a process has multiple start activities with correlation sets then all such activities MUST share at least one common correlationSet and all common correlationSets defined on all the activities MUST have the value of the initiate attribute be set to "join".


59 static analysis For <reply>, if <toPart> elements are used on a <reply> activity then the variable attribute MUST NOT be used on the same activity.


62 static analysis If <pick> has a createInstance attribute with a value of yes, the events in the <pick> MUST all be <onMessage> events.


63 static analysis The semantics of the <onMessage> event are identical to a <receive> activity regarding the optional nature of the variable attribute or <fromPart> elements, if <fromPart> elements on an activity then the variable attribute MUST NOT be used on the same activity (see SA00055).


64 static analysis For <flow>, a declared link's name MUST be unique among all <link> names defined within the same immediately enclosing <flow>.


65 static analysis The value of the linkName attribute of <source> or <target> MUST be the name of a <link> declared in an enclosing <flow> activity.


66 static analysis Every link declared within a <flow> activity MUST have exactly one activity within the <flow> as its source and exactly one activity within the <flow> as its target.


67 static analysis Two different links MUST NOT share the same source and target activities; that is, at most one link may be used to connect two activities.


68 static analysis An activity MAY declare itself to be the source of one or more links by including one or more <source> elements. Each <source> element MUST use a distinct link name.


69 static analysis An activity MAY declare itself to be the target of one or more links by including one or more <target> elements. Each <target> element associated with a given activity MUST use a link name distinct from all other <target> elements at that activity.


70 static analysis A link MUST NOT cross the boundary of a repeatable construct or the <compensationHandler> element. This means, a link used within a repeatable construct (<while>, <repeatUntil>, <forEach>, <eventHandlers>) or a <compensationHandler> MUST be declared in a <flow> that is itself nested inside the repeatable construct or <compensationHandler>.


71 static analysis A link that crosses a <catch>, <catchAll> or <terminationHandler> element boundary MUST be outbound only, that is, it MUST have its source activity within the <faultHandlers> or <terminationHandler>, and its target activity outside of the scope associated with the handler.


72 static analysis A <link> declared in a <flow> MUST NOT create a control cycle, that is, the source activity must not have the target activity as a logically preceding activity.7


73 static analysis The expression for a join condition MUST be constructed using only Boolean operators and the activity's incoming links' status values.


74 static analysis The expressions in <startCounterValue> and <finalCounterValue> MUST return a TII (meaning they contain at least one character) that can be validated as a xsd:unsignedInt. Static analysis MAY be used to detect this erroneous situation at design time when possible (for example, when the expression is a constant).


75 static analysis For the <forEach> activity, <branches> is an integer value expression. Static analysis MAY be used to detect if the integer value is larger than the number of directly enclosed activities of <forEach> at design time when possible (for example, when the branches expression is a constant).


76 static analysis For <forEach> the enclosed scope MUST NOT declare a variable with the same name as specified in the counterName attribute of <forEach>.


77 static analysis The value of the target attribute on a <compensateScope> activity MUST refer to the name of an immediately enclosed scope of the scope containing the FCT-handler with the <compensateScope> activity. This includes immediately enclosed scopes of an event handler (<onEvent> or <onAlarm>) associated with the same scope.


78 static analysis The target attribute of a <compensateScope> activity MUST refer to a scope or an invoke activity with a fault handler or compensation handler.


79 static analysis The root scope inside a FCT-handler MUST not have a compensation handler.


80 static analysis There MUST be at least one <catch> or <catchAll> element within a <faultHandlers> element.


81 static analysis For the <catch> construct; to have a defined type associated with the fault variable, the faultVariable attribute MUST only be used if either the faultMessageType or faultElement attributes, but not both, accompany it. The faultMessageType and faultElement attributes MUST NOT be used unless accompanied by faultVariable attribute.


82 static analysis The peer-scope dependency relation MUST NOT include cycles. In other words, WS-BPEL forbids a process in which there are peer scopes S1 and S2 such that S1 has a peer-scope dependency on S2 and S2 has a peer-scope dependency on S1.8


83 static analysis An event handler MUST contain at least one <onEvent> or <onAlarm> element.


84 static analysis The partnerLink reference of <onEvent> MUST resolve to a partner link declared in the process in the following order: the associated scope first and then the ancestor scopes.


88 static analysis For <onEvent>, the resolution order of the correlation set(s) referenced by <correlation> MUST be first the associated scope and then the ancestor scopes.


91 static analysis A scope with the isolated attribute set to "yes" is called an isolated scope. Isolated scopes MUST NOT contain other isolated scopes.


92 static analysis Within a scope, the name of all named immediately enclosed scopes MUST be unique.


93 static analysis Identical <catch> constructs MUST NOT exist within a <faultHandlers> element.


100 notice Either a non-standard element9 was parsed or a BPEL activity was considered as misplaced. In the first case, a non-standard element was parsed when the parser expected a BPEL standard activity. Then, a syntax error is printed and the whole element is ignored. The parse error and this message can usually be ignored, as non-standard elements would neither we translated to a Petri net model nor are constrained by the WS-BPEL specification.

In the second case, a syntactically correct BPEL was skipped, because it was misplaced. As an example, consider two activities embedded in a <while> activity without an enclosing <sequence> activity. In this case, the second activity triggers this message.


101 notice The <partners> construct (only supported by BPEL4WS 1.1) is skipped due to a syntax error.


102 notice The <to> or <from> construct is skipped due to a syntax error.


103 notice The <condition> construct is skipped due to a syntax error.


104 critical When a syntax error occurs, BPEL2oWFN tries to recover and continues parsing the input file after skipping the faulty or unknown element. Sometimes, however, the skipping of activities yields to situations where a further analysis of the BPEL process is impossible. In this case, the syntax of the process has to be fixed or non-standard elements have to be removed or out-commented.


105 notice When a syntax error occurs, BPEL2oWFN tries to recover and continues parsing the input file after skipping the faulty or unknown element. If it is possible to continue, the analysis results might be faulty. In this case, the syntax of the process has to be fixed or non-standard elements have to be removed or out-commented.


106 warning CFG analysis detected two receiving activities (i.e., <receive>, <onEvent>, <onMessage>, synchronous <invoke>) that might be activated concurrently and share the same partner link, port type, operation, and correlation set. When a message is sent to the process, these activities are in conflict; that is, it is not defined which activity will receive an inbound message. At runtime, the standard fault bpel:conflictingReceive would be thrown.10


107 warning A mandatory attribute of an activity was not defined. Especially for communicating activities, the absence of partnerLink and operation might hamper the subsequent analysis and Petri net generation.


108 syntax An attribute was set to a value that violates the attribute's given type. Only the types tBoolean, tInitiate, tRoles, and tPattern are checked.


109 warning A variable referenced in an activity was not defined before; that is, no matching <variable> definition was found in a parent scope.


110 warning A partner link referenced in an activity was not defined before; that is, no matching <partnerLink> definition was found in the process.


111 warning A correlation set referenced in an activity was not defined before; that is, no matching <correlationSet> definition was found in a parent scope.


112 notice The <literal> construct is skipped due to a syntax error.


113 syntax A UTF-8 character was read in the input file. As BPEL2oWFN's scanner does not support Unicode, all UTF-8 characters are ignored. This message is only displayed when the first UTF-8 character is read.


114 warning CFG analysis detected a read access to a variable that was not initialized before. At runtime, the standard fault bpel:uninitializedVariable would be thrown.11


115 notice The process definition defines an abstract process profile, and thus allows several “opaque” constructs. When processing and analyzing an abstract process, BPEL2oWFN might report error messages that where designed for executable processes, for example missing attributes. Static analysis errors detected in an abstract process are reported as warnings.


116 notice An <opaqueActivity> of an abstract process is modeled by an <empty> activity.


117 notice When using the parameter small, the occurrence of join failures is not modeled. Thus, any activity is treated as if the attribute suppressJoinFailure is set to yes.12


118 notice A user-defined transition condition is ignored and modeled as “n-out-of-n” (true) instead.


119 notice A user-defined transition condition is ignored and modeled as “1-out-of-n” (XOR) instead.


120 notice When using the parameter small, the FTC (fault, termination, and compensation) handlers are not modeled.


121 notice When using the parameter small, activities of the negative control flow (<exit>, <throw>, <compensate>, and <compensateScope>) are replaced by an <empty> activity.


122 notice A syntax error in the BPEL4Chor chorography file occurred.


123 notice A syntax error in the WSDL input file occurred.


124 notice An XML Schema element nested in a WSDL <types> element was ignored. This is usually no problem, as WSDL <types> are not evaluated in subsequent analysis or translation.


125 notice A variable property element was ignored while parsing the input WSDL file.


126 warning A WSDL <message> referenced in a WSDL <operation> was not found.


127 warning A WSDL <portType> referenced in a WSDL <role> was not found.


128 warning A WSDL <operation> referenced in a BPEL activity was not specified in the input WSDL file.


129 warning A WSDL <role> of a partnerLinkType referenced by a <partnerLink> was not defined in the specified <partnerLinkType> in the input WSDL file.


130 warning A WSDL <partnerLinkType> referenced by a <partnerLink> was not specified in the input WSDL file.


131 error An activity has neither a name or id attribute and thus can not be linked with a BPEL4Chor <messageLink>.


132 error An activity has neither could not be linked with a BPEL4Chor <messageLink> using the activity's name or id attribute.


133 notice An <extensionActivity> is replaced by an <opaqueActivity> (cf. notice 116).


134 warning A BPEL4Chor <participantType> was defined twice.


135 warning The <participantType> referenced by a BPEL4Chor <participant> was not found.


136 error The value of a <forEach>'s attribute id or name does not reference a BPEL4Chor <participant> or <participantSet>. Thus, the <forEach> activity is not grounded to the BPEL4Chor topology.


137 error In a BPEL4Chor topology, no XML namespace was defined for a <participant>. In a WS-BPEL file, the attribute targetNamespace could not to be grounded to a BPEL4Chor <participant>.


138 notice In a BPEL4Chor topology, a partner link specified for an activity was not found. Instead, the name of the specified id is used as a partner link.


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4 File Formats

In this chapter, we show how a BPEL process can be translated to a Petri net model an then exported to several output file formats. Consider the following simple BPEL process example.bpel:

     
     <process name="exampleprocess" targetNamespace="www.gnu.org/software/bpel2owfn">
       <partnerLinks>
         <partnerLink name="PL" partnerLinkType="PLT"
           myrole="exampleprocess" partnerRole="exampleuser" />
       </partnerLinks>
     
       <sequence>
         <receive partnerLink="PL" operation="req" createInstance="yes" />
         <reply partnerLink="PL" operation="ack" />
       </sequence>
     </process>
     

This process just waits for a message req on partner link PL and replies to this message with ack on the same partner link. To parse this BPEL process, BPEL2oWFN has to be invoked with

     bpel2owfn -i example.bpel

which responds with the output:

     
     ==============================================================================
     GNU BPEL2oWFN 2.0.1 reading from file `example.bpel'
     ------------------------------------------------------------------------------
     ------------------------------------------------------------------------------
     3 activities (2 basic, 1 structured, 0 scopes) + 3 implicit activities
     0 handlers (0 FH, 0 TH, 0 CH, 0 EH) + 1 implicit handlers
     0 links, 0 variables
     
     [SYNTAX ANALYSIS] No syntax errors found.
     [STATIC ANALYSIS] No errors found checking 44 statics analysis requirements.
     [OTHER ANALYSIS]  No other errors found.
     ------------------------------------------------------------------------------
     

This means, the process consists of three activities (two basic activities and one structured activities), no handlers, no links and no variables. On the bottom the analysis results are summarized: no syntactic, static, or other error was found.

Furthermore, three “implicit” activities are counted: The WS-BPEL specification describes several implicit transformations of the input process, as well as standard fault, termination and compensation handlers. In the considered BPEL process, no fault handlers are specified. Thus, a standard fault handler is added by BPEL2oWFN:

     <faultHandlers>
       <catchAll>
         <sequence>
           <compensate />
           <rethrow />
         </sequence>
       </catchAll>
     </faultHandlers>

To see how the BPEL process looks like after applying the transformation rules and adding the standard handlers, BPEL2oWFN output the manipulated process using its pretty-printer:

     bpel2owfn -i example.bpel -m pretty

The manipulated process looks like this:

     
     <process id="1" abstractProcess="no" exitOnStandardFault="no" name="exampleprocess"
      suppressJoinFailure="no" targetNamespace="www.gnu.org/software/bpel2owfn">
       <partnerLinks>
         <partnerLink id="3" myrole="exampleprocess"
            name="PL" partnerLinkType="PLT" partnerRole="exampleuser" />
       </partnerLinks>
       <faultHandlers id="4">
         <catchAll id="13">
           <sequence id="12" suppressJoinFailure="no">
             <compensate id="11" suppressJoinFailure="no">
             </compensate>
             <rethrow id="10">
             </rethrow>
           </sequence>
         </catchAll>
       </faultHandlers>
       <sequence id="7" suppressJoinFailure="no">
         <receive id="8" createInstance="yes" operation="req"
            partnerLink="PL" suppressJoinFailure="no">
         </receive>
         <reply id="9" operation="ack" partnerLink="PL" suppressJoinFailure="no">
         </reply>
       </sequence>
     </process>
     

Each activity is printed together with its attributes. Note that the standard values of several attributes (e.g., abstractProcess or suppressJoinFailure) are added. Furthermore, an identifier (attribute id) was added to every activity.

We now want to create a compact Petri net model of the BPEL process, using the petrinet mode and the small parameter:

     bpel2owfn -i example.bpel -m petrinet -p small

BPEL2oWFN now also displays statistics of the generated Petri net model:

     |P|=5, |P_in|= 1, |P_out|= 1, |T|=2, |F|=6

The generated Petri net model consists of five places, including one input and one output place, two transitions and six arcs. To create a graphical representation, invoke BPEL2oWFN with the following options:

     bpel2owfn -i example.bpel -m petrinet -p small -f dot -o

This command creates a file example.dot, containing a Graphviz dot representation of the Petri net, and—if the dot tool was found in the search path—a PNG (Portable Network Graphics) an image file example.png. The latter looks like this:

images/example.png

The graphic depicts the generated open workflow net. The inner of the net, that is, all nodes except the interface places, are depicted inside the dashed box, whereas the interface is depicted outside the frame. Input places and all connected transitions are colored orange. Similarly, output places and connected transitions are colored yellow. Gray places belong to the final marking, that is, the marking [p3] is the final marking of the oWFN.

To reach this final marking, the environment has to send a message in.PL.req, followed by receiving a message out.PL.ack. The name of the communication places is composed by the communication direction (“in” or “out”), the partner link's name (PL) and the operations name (req or ack).

For this very small process, it is easy to validate the generated Petri net model, that is, to compare the intended semantics by the actually modeled semantics. Especially the correlation between the nodes of the Petri net and the activities of the input BPEL process is not obvious for larger processes. To this end,

     bpel2owfn -i example.bpel -m petrinet -p small -f info

displays an information file, consisting of all the Petri net nodes' roles.

     
     PLACES:
     ID      TYPE            ROLES
     p1      internal        1.internal.initial
                             7.initial
                             7.internal.initial
                             8.initial
                             8.internal.initial
     p2      internal        8.final
                             8.internal.final
                             9.initial
                             9.internal.initial
     p3      internal        1.internal.final
                             7.final
                             7.internal.final
                             9.final
                             9.internal.final
     in.PL.req       input           in.PL.req
     out.PL.ack      output          out.PL.ack
     
     TRANSITIONS:
     ID      ROLES
     t1      8.internal.receive
     t2      9.internal.reply
     

This file has to be read as follows: the place p1 has the type internal (i.e., is not connected with an interface place) and has the roles 1.internal.initial, 7.initial, 7.internal.initial, 8.initial, and 8.internal.initial. While the prefix of each role is the identifier of an activity (1 for the <process>, 7 for the <sequence>, and 8 for the <receive>), the suffix specifies the role inside the respective pattern. Without going too much into details, 1.internal.initial is the role of the initial place of the pattern for the <process>, whereas, for example 7.internal.final is the final place of the <sequence>'s pattern. Similarly, roles of transitions are specified. Multiple roles of a single place arise due to the merging of distinct places during the composition of the several patterns.

Now that we have convinced ourselves that the generated net reflects the intended behavior of the BPEL process, we can export the Petri net model to an output file to process it by analysis tools. In this case, we want to create a Fiona open workflow net executing

     bpel2owfn -i example.bpel -m petrinet -p small -f owfn -o

which creates a file example.owfn:

     
     {
       generated by: BPEL2oWFN 2.0.1
       input file:   `example.bpel' (process `exampleprocess')
       invocation:   `bpel2owfn -i example.bpel -m petrinet -p small -f owfn'
       net size:     |P|=5, |P_in|= 1, |P_out|= 1, |T|=2, |F|=6
     }
     
     PLACE
       INTERNAL
         p1, p2, p3;
     
       INPUT
         in.PL.req {$ MAX_OCCURRENCES = 1 $};
     
       OUTPUT
         out.PL.ack {$ MAX_OCCURRENCES = 1 $};
     
     
     INITIALMARKING
       p1:    1 {initial place};
     
     FINALMARKING
       p3 {final place};
     
     
     TRANSITION t1 { input }
       CONSUME in.PL.req, p1;
       PRODUCE p2;
     
     TRANSITION t2 { output }
       CONSUME p2;
       PRODUCE out.PL.ack, p3;
     
     
     { END OF FILE `example.owfn' }
     

This is finally the oWFN model of the BPEL process that can be analyzed by Fiona13.


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5 FAQ and Known Bugs

5.1 Frequently Asked Questions

5.2 Known Bugs

Though this is the second major release version of BPEL2oWFN, it might still contain poorly tested, inefficient code.

5.3 Reporting Bugs

If you find a bug in BPEL2oWFN or have a question, please first check that it is not a known bug or a frequently asked question listed in above. Otherwise, please send us an email to bug-bpel2owfn@gnu.org. 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.

5.4 Contact Person

Niels Lohmann

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

Homepage
http://www.informatik.hu-berlin.de/top/mitarbeiter/lohmann
E-mail
nlohmann@informatik.hu-berlin.de
Skype
nlohmann
Phone
(+49) (30) 2093-3070
Fax
(+49) (30) 2093-3067

5.5 Help BPEL2oWFN

BPEL2oWFN is now developed for one and a half year, and grown to a quite big program. Since November 2006, BPEL2oWFN is a GNU package, and the development is organized at Savannah (https://savannah.gnu.org/projects/bpel2owfn). We are always looking for developers and testers that can help us improving BPEL2oWFN.


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Appendix A GNU Free Documentation License

Version 1.2, November 2002
     Copyright © 2000,2001,2002 Free Software Foundation, Inc.
     51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.
  1. PREAMBLE

    The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

    This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

  2. APPLICABILITY AND DEFINITIONS

    This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

    A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

    A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

    The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

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    The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

    A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

    The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

  3. VERBATIM COPYING

    You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

    You may also lend copies, under the same conditions stated above, and you may publicly display copies.

  4. COPYING IN QUANTITY

    If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

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    It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

  5. MODIFICATIONS

    You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

    1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
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    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
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    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
    8. Include an unaltered copy of this License.
    9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
    10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
    11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
    12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
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    14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
    15. Preserve any Warranty Disclaimers.

    If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

    You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

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  6. COMBINING DOCUMENTS

    You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

    In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”

  7. COLLECTIONS OF DOCUMENTS

    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

  8. AGGREGATION WITH INDEPENDENT WORKS

    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

  9. TRANSLATION

    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

  10. TERMINATION

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  11. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  year  your name.
       Permission is granted to copy, distribute and/or modify this document
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       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
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If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

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If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.


Footnotes

[1] Fiona is available at http://www.informatik.hu-berlin.de/top/tools4bpel.

[2] This mode was formally called consinstency.

[3] This mode was formally called communicationonly.

[4] Yasper is available at http://www.yasper.org.

[5] The descriptions for static analysis messages are taken from Appendix B of the WS-BPEL specification.

[6] The specification describes all allowed combinations of elements and attributes in from- and to-specifications.

[7] This fault can only be detected in mode mode cfg.

[8] This fault can only be detected in mode mode cfg.

[9] All elements that are not explicitly defined in the WS-BPEL specification (e.g., elements from other namespaces) are considered as “non-standard”.

[10] This fault can only be detected in mode mode cfg.

[11] This fault can only be detected in mode mode cfg.

[12] If the attribute suppressJoinFailure is not explicitly defined for an activity, the value is inherited by the parent activity.

[13] Fiona is available at http://www.informatik.hu-berlin.de/top/tools4bpel.