1. Undoing Event-driven Adaptation
of Business Processes
Sébastien Mosser, Gabriel Hermosillo, Anne-Françoise Le Meur,
Lionel Seinturier, Laurence Duchien
INRIA Lille-Nord Europe, University Lille 1, LIFL (UMR CNRS 8022)
8th International Conference on Services Computing
Washington DC, July 5th 2011

2. Big Picture: Adaptation
System
T0
2

3. Big Picture: Adaptation
System
T0 T1
2

4. Big Picture: Adaptation
System
T0 T1 T2
2

5. Big Picture: Adaptation
System
T0 T1 T2 T3
2

6. Big Picture: Adaptation
System
T0 T1 T2 T3 ...
2

7. Question: How To Unadapt? (e.g., remove )
... Tn-1 Tn
3

8. Question: How To Unadapt? (e.g., remove )
only if
depends on
depends on and
... Tn-1 Tn System
3

9. Towards Unadaptation: From «Do» to «Undo»
• Goal:
• Produce a system «as it would be if this adaptation had never
happened»
• Challenges:
• Identify the «undo» trigger event
• Identify correlated adaptations (to be removed too)
• Yield the expected system
4

10. Outline
• Context:
• Business Process Adaptation & Complex Event Processing
• Contribution: From Adaptation to Automated Unadaptation
(1) Identifying the trigger event
(2) Identify correlated adaptations
(3) Yield the system, «as it would be if this adaptation had never happened»
• Demonstration
• Conclusions & Perspectives
5

11. Context:
Business Process Adaptation
& Complex-event Processing

12. Business Process
Activity
Login
Causal
Request
Relationship
Search
Display
Logout
Used to express behavior in the
Service-oriented Architecture paradigm
Industrial standard: BPEL
7

13. Business Processes Adaptation
Login Backup
Request
Search
Display
Logout
search_status ≠ ok ( )
Adaptation: «use the backup server»
8

14. From Event to Complex Event Processing
• Event processing:
search_status ≠ ok
• Boolean formula applied to sensor values
• Event compositions:
• Logical connectors: conjunction ( ∧ ), disjunction ( ∨ ) = ;
• Temporal connectors: sequence («followed by»), time window («within»)
9

15. Event-Driven Adaptation of Business Processes
e.g., Aspects
Sensors
e.g., BPEL
e.g., ESPER
10

16. Running Example
1. «Fail» event detected (search service encounters errors):
‣ The system uses now a backup server, off-site
2. «Slow» event detected (bandwidth drops)
‣ «Cache» event is identified («fail; slow»)
‣ A cache is introduced
3. «Perf» event detected (CPU overload)
‣ Monitoring is inserted in the system
4. Search service is now ok ... What should we do?
11

17. Reminder: Unadaptation Challenges
#1: Identify the
trigger event
???
#2: Identify correlated #3: Yield the system
adaptations
12

18. Contribution #1:
Identifying the trigger event

19. Running Example
fail «system uses backup» undo
: search_status ≠ 200
14

20. Running Example
fail «system uses backup» undo
: search_status = 200 : search_status ≠ 200
¬fail fail
... ...
14

21. Running Example
fail «system uses backup» undo
: search_status = 200 : search_status ≠ 200
¬fail fail
... ...
-1
fail = fail ; ¬fail 14

22. Definition: Complex Event ( ε ) & Opposite ( ¬ε )
Trigger event: ε = ε ; ¬ε
-1
15

23. Contribution #2:
Identify Correlated Adaptations
depends on depends on
and
only if

24. Idea: «prune the adaptation sequence»
• Identify in the adaptation history, for a given event ε:
• The correlated events (now irrelevant after ε vanishment)
• The orthogonal events (still relevant, even after ε vanishment)
17

25. Running Example
do undo
prune( [ , , , ], [ ]) cache slow
=[ | prune( [ , , ], [ ]) ] = ;
fail
18

26. Running Example
do undo
prune( [ , , , ], [ ]) cache slow
=[ | prune( [ , , ], [ ]) ] = ;
fail
=[ | prune( [ , ], [ , ]) ]
=[ , | prune( [ ], [ , ])]
=[ , , | prune([ ], [ , ]) ]
Still relevant =[ , , ] Correlated 18

27. Contribution #3:
Yield the system,
«as it would be if this adaptation had never happened»
Sn-1 Sn

28. Action-based Representation (e.g., Praxis, Adore)
[Blanc et al, ICSE’08]
[Mosser et al, TAOSD’11]
a1
p = [ add(a1), add(a2), add(a3),
add(a1→a2), add(a2→a3) ]
a2
a3
p 20

29. Action-based Representation (e.g., Praxis, Adore)
[Blanc et al, ICSE’08]
[Mosser et al, TAOSD’11]
a1
p = [ add(a1), add(a2), add(a3),
add(a1→a2), add(a2→a3) ]
a2 a’2
backup server invocation
p = [ add(a1), add(a2), add(a3),
a3 add(a1→a2), add(a2→a3)]
● [ add(a’2), add(a1→a’2), add(a’2→a3),
p del(a1→a2), del(a2→a3), del(a2) ] 20

30. «To adapt» = «To produce actions»
Adaptation function (φ) rational:
«generate the actions needed to adapt»
p = [ add(a1), add(a2), add(a3),
add(a1→a2), add(a2→a3) ]
a1 φ(p) = [ add(a’2), add(a1→a’2), add(a’2→a3),
del(a1→a2), del(a2→a3), del(a2) ]
a2 a’2
Adaptation:
a3
(1) compute the adaptation, (2) execute it. 21

31. Process Rewind to Forget Adaptations
-1 -1
add( X ) → del( X ) del( Y ) → add( Y )
p = [ add(a1), add(a2), add(a3),
add(a1→a2), add(a2→a3)]
a1
● [ add(a’2), add(a1→a’2), add(a’2→a3),
a2 a’2 del(a1→a2), del(a2→a3), del(a2) ]
a3
22

32. Process Rewind to Forget Adaptations
-1 -1
add( X ) → del( X ) del( Y ) → add( Y )
p = [ add(a1), add(a2), add(a3),
add(a1→a2), add(a2→a3)]
a1
● [ add(a’2), add(a1→a’2), add(a’2→a3),
a2 del(a1→a2), del(a2→a3), del(a2) ]
● [ add(a2), add(a2→a3), add(a1→a2),
a3 del(a’2→a3), del(a1→a’2), del(a’2) ]
22

33. Global Undo Mechanism:
S0 S1 S2 S3 S4 S5 S6
23

34. Global Undo Mechanism:
S0 S1
(rewind)
S2
23

35. Global Undo Mechanism:
S0 S1
(rewind)
S2
(prune) [ , , ] FORGET
23

36. Global Undo Mechanism:
S0 S1
(rewind)
S2
(prune) [ , , ] FORGET
(replay) S7
S’3 S’5 23

37. Re-«play» Implies to Re-«adapt»
S7 = φ ( φ ( φ ( S2 )))
S2 S7
May adapt elements
introduced by other
adaptations
Impossible to «simply» replay the preexisting sequence 24

38. Demonstration: http://bit.ly/scc11

39. Events & Adaptation Implementation
26

40. Event-driven Adaptation
27

41. Automated Unadaptation
28

42. Conclusions & Perspectives

43. Conclusions
• Fact: naive unadaptation may lead to corrupted processes !
• Proposal: Automated unadaptation
• Identify the triggering event
• Identify the correlated adaptations
• Yield the system, «as it would be if this adaptation had never happened»
• Generic mechanisms (platform-independent implementation)
30

44. Upcoming Perspectives
• From processes to running instances
• Long-living processes will require unadaptation at instance level
• Instances must be adapted with care (e.g., execution pointer)
• Software Engineering & Software Evolution
• From refactoring to un-refactoring
• From pattern introduction to pattern removal
31

45. Graphics: sxc.hu & C.line
Thank You for Your Attention !
Undoing Event-driven Adaptation
of Business Processes
Sébastien Mosser, Gabriel Hermosillo, Anne-Françoise Le Meur,
Lionel Seinturier, Laurence Duchien