The document describes a model-driven approach to implementing coordination protocols in BPEL. It presents a method to model coordination protocols as Coordination Protocol Graphs (CPGs) and then automatically generate abstract BPEL processes for the coordinator and participants. These abstract processes are then manually refined into executable BPEL code. The approach represents states and transitions for participants as BPEL processes and uses events and conditions to model the coordinator's management of registrations, activations, and protocol completion. The conclusion discusses future work on supporting loops, coordinator hierarchies, and mixed protocols.

1. 1st International Workshop on Model-Driven Engineering
for Business Process Management (MDE4BPM 2008)
A Model-Driven Approach to Implementing
Coordination Protocols in BPEL
Oliver Kopp, Branimir Wetzstein, Ralph Mietzner, Stefan Pottinger,
Dimka Karastoyanova, Frank Leymann
Institute of Architecture of Application Systems
kopp@iaas.uni-stuttgart.de

2. Agenda
Background
Coordination in a Web Service World
Transaction Research Roadmap of the IAAS
The Approach
Conclusion and Outlook
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 2

3. Modeling Coordination
Protocols
© Oliver Kopp 3

4. Modeling Coordination Protocols – 1/4
Describe states and transitions of one participant
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 4

5. Modeling Coordination Protocols – 2/4
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 5

6. Modeling Coordination Protocols – 3/4
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 6

7. Modeling Coordination Protocols – 4/4: WS-BA
Coordination
Protocol Graph
CPG
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 7

8. WS-Coordination
Web Services Coordination (WS-Coordination) Version 1.1
One coordinator for many participants
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 8

9. Background
© Oliver Kopp 9

10. Research at IAAS
Aim: Describe any coordination protocol by BPEL
Rania Khalaf’s protocol for split loops and scopes
Supporting Business Process Fragmentation While Maintaining Operational
Semantics: A BPEL Perspective, Dissertation, University of Stuttgart
Auctions – e.g., multiple round sealed auction
F. Leymann and S. Pottinger: Rethinking the Coordination Models
of WS-Coordination and WS-CF, ECOWS’05
Mapping of OASIS-BTP and WS-CAF to
WS-Coordination (Master’s Thesis)
Replacement of BPEL’s WS-BA transaction behavior by
arbitrary transaction behavior
Externalization of BPEL’s transaction behavior
S. Pottinger, R. Mietzner and F. Leymann:
Coordinate BPEL Scopes and Processes by Extending the WS-
Business Activity Framework, CoopIS 2007
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 10

11. Why BPEL?
BPEL is on a higher level than usual
programming languages
BPEL has native support for
Concurrency
Forward and backward recovery
Fault handler to catch fault and do alternative action
Phoenix behavior: If BPEL engine crashes, the state before
the crash is restored
Scalability
BPEL is supported by the most important
vendors
IBM, Oracle, Microsoft, Sun, …
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 11

12. The Approach
© Oliver Kopp 12

13. Overview
• Domain-specific Language
CPG (Coordination Protocol Graph)
• Platform-Independent Model
• Marking: WSDL names
Abstract Abstract WSDL • Automatic generation from CPG
Coordinator Participant Definitions • Abstract BPEL processes
Process Process • WSDL interfaces for coordinator and
Model Model participant process
Executable Executable • Manual refinement from abstract BPEL
Coordinator Participant processes
Process Process • Replacing opaque tokens with
Model Model concrete BPEL code
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 13

14. Participant
© Oliver Kopp 14

15. Observations and Basic Idea
Participant is in one state at a time
BPEL supports graph-based programming
A CPG is a graph
Translate Graph Structure as Close as Possible
to BPEL
“Element Preservation Strategy” in
J. Mendling, K.B. Lassen, and U. Zdun. On the
Transformation of Control Flow between Block-
Oriented and Graph-Oriented Process Modeling
Languages. IJBPIM, 3(2), September 2008.
No loops
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 15

16. WS-BA with Participant Completion
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 16

17. Implementation in BPEL
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 17

18. State Canceling
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 18

19. State Completed
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 19

20. State Active
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 20

21. State Active simplified
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 21

22. Coordinator
© Oliver Kopp 22

23. Observations and Basic Idea
Coordinator has to hold state for each participant
Participant can register at any time
Not specified how to end coordination
Impossible to keep graph-structure
Generate code for managing
Activation
Registration
End of Coordination
Use Event-Condition-Action idea
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 23

24. Activation and Registration Services
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 24

25. Overview of the Coordinator
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 25

26. Reaction to message “fail”
If sending participant in state “Active”
Set flag “failed” to true
For all participants in state “Active”
Send “Cancel”
For all participants in state “Completed”
Send “Compensate”
Send “Failed”
Else
Fail came from Canceling or Compensating
No action required
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 26

27. Conclusion
© Oliver Kopp 27

28. Conclusion and Outlook
MDA approach for WS-Coordination
Generated BPEL Skeletons
Participant easy to complete
Coordinator less easy to complete
Loops
Jussi Vanhatalo, Hagen Völzer, Jana Koehler. The
Refined Process Structure, BPM 2008
W. Zhao, R. Hauser, K. Bhattacharya, B. R. Bryant, F.
Cao. Compiling business processes: untangling
unstructured loops in irreducible flow graphs. International
Journal of Web and Grid Services, 2006
Support of Coordinator Hierarchy
Support of mixed protocols at a coordinator
WS-BA and WS-AT
A Model-Driven Approach to Implementing Coordination Protocols in BPEL presented by Oliver Kopp 28