This document describes a Petri net semantics for the WS-BPEL specification. It presents a formal model of open workflow nets to represent WS-BPEL processes. This semantics maps WS-BPEL activities like receive, flow, and scope to patterns in open workflow nets. The semantics allows formal analysis of WS-BPEL processes and has been implemented in a tool that converts BPEL processes to Petri nets.

2. WS-BPEL
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
 Web Service Business Process Execution Language
 Language
to describe business processes
implemented as Web services
 Described as XML document
<process name="example">
<sequence>
<receive partnerLink="p1" />
<invoke partnerLink="p2" />
<reply partnerLink="p1" />
</sequence>
</process>
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3. Petri Net Semantics for WS-BPEL
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
 Goal:
a formal semantics for WS-BPEL
… to understand WS-BPEL
… to analyze WS-BPEL processes
 Formal model: open workflow nets
workflow nets
+ interface
– structural constraints
= open workflow nets
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4. Example: <receive> Activity
initial
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
stop
t4
channel
x
t1
x
running x
t5
x x
x variable
v
t2 y
stopped
t3 faulted t6
faultName
t7
failed
final
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5. Example: <flow> Activity
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
initial
stop
t1 t3
running t4
A B
t5
sync
stopped
t6
final 5

6. New Features of WS-BPEL 2.0
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
 Semanticclarifications
 What happens during compensation?
 Syntactic
sugar
 <repeatUntil> activity, inline validation, …
 Some new activities and features
 <forEach> activity, termination handlers, ...
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7. Implementation
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
BPEL2oWFN
meta model Petri net model
Abstract Petri Net
Syntax Tree API
BPEL process Petri net
Control/Data Pattern
Input Formats: Flow Graph Repository Output Formats:
 WS-BPEL 2.0  Fiona oWFN
static analysis pattern selection
 BPEL4WS 1.1  LoLA
 Abstract WS-BPEL 2.0  PNML
 BPEL4Chor  INA, PEP, SPIN
 WSDL 1.1  …
http://www.gnu.org/software/bpel2owfn
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8. Applications of the Semantics (1)
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
Open workflow nets allow for…
 Analysis of the inner of the oWFN (w/o interface)
 Deadlock freedom
 (relaxed) Soundness
 Temporal logics
 …
 Analysis results can be mapped back to WS-BPEL
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9. Tools4BPEL Tool Chain (1)
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
BPEL2oWFN
WS-BPEL Petri Net
Process Model
LoLA2BPEL LoLA
Witness
Path
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10. Applications of the Semantics (2)
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
Open workflow nets allow for…
 Analysis of the open workflow net
 Consistency
 Controllability
 Partner synthesis
 …
 Synthesis results can be re-translated to WS-BPEL
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11. Tools4BPEL Tool Chain (2)
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
BPEL2oWFN
WS-BPEL oWFN
Process Model
oWFN2BPEL Fiona
Partner
oWFN
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12. Summary (1)
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
 Feature-complete semantics for WS-BPEL 2.0
and its predecessor specification
 Simplified patterns for important constructs
Case study:
Old Semantics New Semantics
Places 410 242
Transitions 1,069 397
States 6,261,648 304,007
 Compiler BPEL2oWFN
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13. Summary (2)
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
 Petri
net semantics allows to formally analyze
WS-BPEL processes
 Analysis results can be re-translated into WS-BPEL
 Completetool chains help to “conceal” formal
methods from the WS-BPEL designer
 Danger:
new semantics needed for future versions
WS-BPEL 2.1, WS-BPEL 3.0, WS-BPEL 4.0, …
Thank you very much! 13

15. Parallel <forEach>
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
initial
initialize
running
stop1
initial stop stop
stop3 x
b stop2
stopped active
stopping
t1
stopped
scope
Successful x=0
skipping
all stopped
x
t2
x
!Successful x=0 c
x-1 counter
finish2
t3 x
final x>0
t4 finish1
done
instance 1
final
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16. <scope>
A Feature-Complete Petri Net Semantics for WS-BPEL 2.0
!Exiting Exiting
initial fault in ch fault up compensate
Active
fn fn inner stopped
fn
fn ignore
fault
!Active initialize Active term Successful !Successful Active !Active
pass
handle
fn !Active start ch skip ch start th skip th
inner
fsave stopped stop
stop stop ch stop stop
inner activity inner activity of the
stopped skip ch stopped termination stopped
and stopped fault handlers compensation
handler
event handlers handler stopped
fault in fault up fn fault up
ch fault up
final compensated stopped
finalize
fn fn
!Successful Successful
final ch fault in compensated
positive control flow fault handling compensation handling termination handling
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