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.
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.
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.
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:
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 f�r Bildung und Forschung. See http://www.informatik.hu-berlin.de/top/tools4bpel for details.
| 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.
|
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).
BPEL2oWFN supports the following command-line options:
stdin). Wildcards such as process*.bpel are also allowed.
stdout).
stderr).
Debug level:
When invoking BPEL2oWFN several modes are possible.
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.
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.
These options control some Petri net-related options.
<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.
<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.
If you want to enable more than one parameter you have to add -p/ --parameter to each parameter.
Especially for the Petri net mode, a variaty of output formats are supported. There are invoked by the following option:
<type> tag
which is only supported by Yasper4. When the parameter -o is used, a
file with the suffix .pnml is created.
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.
In this section we show some examples how BPEL2oWFN can be invoked. See File Formats for more examples.
dot which layouts the Petri net and creates an output
PostScript file sample.ps.
Further examples for invocations of BPEL2oWFN can be found in the tests directory of the source distribution.
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 |
| 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.
|
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:
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.
BPEL2oWFN uses Flex and Bison to implement the parser. We decided do not use an off-the-shelf XML parser generator as we did not found a suitable platform-independent parser generator whose license was “compatible” to the GNU GPL (General Public License). Furthermore, we use the term generator Kimwitu++ to describe and process the AST (abstract syntax tree), and the trio Flex/Bison/Kimwitu++ integrates seamlessly. Though the grammar has to be defined manually, the generated parser is very flexible as it allows to process BPEL4WS 1.1, WS-BPEL 2.0, and to some extend BPEL4WS 1.0 processes.
However, the parser does not support XML namespaces. BPEL2oWFN will ignore namespace prefixes and skip all elements that are not explicitly covered by the WS-BPEL 2.0, BPEL4WS 1.2 or WSDL 1.1 specification, respectively. Nevertheless, skipping elements are reported as syntax error message (cf. warning message [W00104]).
As a solution, try removing or commenting non-standard elements.
Well, because there are such errors. Many BPEL editors generate invalid BPEL. Even the official WS-BPEL 2.0 specification contains processes with syntax errors. Furthermore, a lot of syntax errors cannot be covered with XSD (XML Schema Definition) validation. Even if the considered process run on existing engines, BPEL2oWFN might reject it, as it stubbornly follows the WS-BPEL specification.
This problem occurs using a pre-compiled windows version of BPEL2oWFN. The generated files are in Windows format, yet LoLA only supports files in Unix format. To overcome this limitation of LoLA, use a tool like dos2unix or change the file format in an editor like vi.
Though this is the second major release version of BPEL2oWFN, it might still contain poorly tested, inefficient code.
Diagnosis: The implemented semantics of was mainly created to support executable BPEL processes. Therefore, the translation of abstract BPEL processes (formerly called business protocols) might be buggy. In particular, the allowed absence of implementation details hampers the analysis of the process and the generation of a formal model.
Solution: To avoid errors, at least each communicating activity should be
defined with partnerLink and operation attribute, and
<invoke> activities should be defined with inputVariable and/or
outputVariable to distinguish the respective asynchronous and synchronous
occurrence.
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 [email protected]. 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 [email protected].
Niels Lohmann
Humboldt-Universität zu Berlin
Institut für Informatik
Unter den Linden 6
10099 Berlin, Germany
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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[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.