Implementing Transactions in JOIN Calculus

1
Theoretical Foundations for Compensations in Flow
Composition Languages
Hernán Melgratti Joint work with Roberto Bruni
and Ugo Montanari Dipartimento di Informatica -
Università di Pisa
2
Motivations Web Service Composition

• Defining complex services as aggregations of
  simpler services
• Interaction based Composition, Conversational
  Patterns or Global Model
• Services describe the ways they can be engaged in
  a larger process
• Flow Composition or Hierarchical Patterns
• Similar to workflow systems a process describes
  the flow of both control and data among WS

3
Motivations Flow Composition
A3
A2
A1
A5
A4
4
Motivations Transactional Flow
Transactional Process
A3
A2
A1
A5
A4
5
Motivations Compensation
Transactional Process
A3
A2
B3
B2
A1
A5
B1
B5
A4
B4
6
Motivations Compensation Flow
Transactional Process
A3
A2
B3
B2
A1
A5
B1
B5
A4
B4
7
Outline of the talk

• Sequential Sagas
• Graphical representation
• Syntax and Semantics
• Adequacy results
• Parallel Sagas
• Nested Sagas
• Additional features
• Concluding remarks

8
Sequential Sagas Graphical Repr.
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9
Sequential Sagas Syntax
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(Step) X 0 A AB (Process) P X
PP (Saga) S P
10
Sequential Sagas Syntax
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S AORO UCRM POUS
(Step) X 0 A AB (Process) P X
PP (Saga) S P
11
Sequential Sagas Semantics

• An activity A either
• commits (A ? )
• aborts (A ? )
• ? A1 ? ,, An ?

12
Sequential Sagas Semantics

• A saga S P under ? either
• commits ( )
• aborts ( )
• fails ( )
• ? is the observable flow

?
? S ??
?
?
? S ??
?
?
? S ??
?

13
Sequential Sagas Semantics

• A process P under ? either
• commits (
  )
• aborts ( )
• fails ( )
• ß and ß are the installed compensations

14
Sequential Sagas Semantics
(saga)
15
Sequential Sagas Semantics
(saga)
(zero)
16
Sequential Sagas Semantics
(saga)
(zero)
(s-act)
17
Sequential Sagas Semantics
(saga)
(zero)
(s-act)
?
? ltß,0gt ?? lt , 0gt
?
(s-cmp)
?
A ? , ? ltAB,ßgt ?? lt , 0gt
?
?
? ltß,0gt ?? lt , 0gt
?
(f-cmp)
?
A ? , ? ltAB,ßgt ?? lt , 0gt
?

18
Sequential Sagas Semantics
?
?
? ltQ,ßgt ?? lt ,ßgt
? ltP,ßgt ?? lt ,ßgt
?
?
(s-step)
??
? ltPQ, ßgt ?? lt ,ßgt
?
?
? ltP,ßgt ?? lt , 0gt
?
(a-step)
?
? ltPQ,ßgt ?? lt ,0gt
?
?
? ltP,ßgt ?? lt , 0gt
?

(a-step)
?
? ltPQ,ßgt ?? lt ,0gt
?

19
Sequential Sagas Adequacy Theorem
?
and ? A1An
? S ??
?
A1
Aj
Ak
An
20
Sequential Sagas Adequacy Theorem
?
and ? A1An
? S ??
?
A1
Aj
Ak
An
?
and ? A1Ak-1Bk-1B1
? S ??
?
Ak
A1
Aj
An
Bj
B1
21
Sequential Sagas Adequacy Theorem
?
and ? A1An
? S ??
?
A1
Aj
Ak
An
?
and ? A1Ak-1Bk-1B1
? S ??
?
Ak
A1
Aj
An
Bj
B1
?
and ? A1Ak-1Bk-1Bj1
? S ??
?

A1
Aj
Ak
An
Bj
B1
22
Parallel Sagas Graphical Representation
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23
Parallel Sagas Syntax
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(Step) X 0 A AB (Process) P X PP
PP (Saga) S P
24
Parallel Sagas Syntax
Update Credit
Refund Money
Accept Order
Refuse Order
Prepare Order
Update Stock
S AORO UCRM POUS
(Step) X 0 A AB (Process) P X PP
PP (Saga) S P
25
Parallel Sagas The Naïve Way
B1
Bj
Bn
B1
Bj
A1
A2
A1
C1
Ck
Cm
C1
Ck
Cm
A1(B1Bj-1Bj-1B1 C1CmCmC1)A1
26
Parallel Sagas Revised
B1
Bj
Bn
B1
Bj
A1
A2
A1
C1
Ck
Cm
C1
Ck
Cm
A1(B1Bj-1Bj-1B1 0)A1
A1(B1Bj-1Bj-1B1 C1C1)A1

A1(B1Bj-1Bj-1B1 C1CmCmC1)A1
27
Parallel Sagas Semantics

• A process P under ? either
• commits (
  )
• aborts ( )
• fails ( )
• is forced to abort (
  )
• is forced to fail (
  )
• ? is the observable concurrent flow

?
? ltP,ßgt ?? lt ,ßgt
?
?
? ltP,ßgt ?? lt , 0gt
?
?
? ltP,ßgt ?? lt , 0gt
?

?
? ltP,ßgt ?? lt , 0gt
?
?
? ltP,ßgt ?? lt , 0gt
?
28
Parallel Sagas Semantics
?
? ltP,0gt ?? lt?, ßgt
? ? , ,
?
(saga)

?
? P ?? ?
?
(forced-abt)
(forced-abt)
29
Parallel Sagas Semantics
(s-par)
30
Parallel Sagas Semantics
(c-par)
?1, ?2 ? ,
?
?
?
? ltP,0gt ?? lt?1,0gt
? ltQ,0gt ?? lt?2,0gt
? ltß,0gt ?? lt ,0gt
?
?
?
?? ?
? ltPQ, ßgt ???? lt ?1 ? ?2 , 0gt
?
?

?
?
?
?







31
Parallel Sagas Semantics
(c-par)
?1, ?2 ? ,
?
?
?
? ltP,0gt ?? lt?1,0gt
? ltQ,0gt ?? lt?2,0gt
? ltß,0gt ?? lt ,0gt
?
?
?
?? ?
? ltPQ, ßgt ???? lt ?1 ? ?2 ? , 0gt
?
?

?
?
?
?







32
Parallel Sagas Semantics
(f-par)
?1 ? ,
?
?

? ltP,0gt ?? lt?1,0gt
? ltQ,0gt ?? lt?2,0gt
?
?
?2 ? , , ,

??
? ltPQ, ßgt ??? lt ?1 ? ?2 , 0gt
?
?

?
?
?
?







33
Parallel Sagas Adequacy
Completion
34
Parallel Sagas Adequacy
Successful Compensation
35
Parallel Sagas Adequacy
Failed Compensation
36
Nested Sagas Graphical Representation
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Add Points
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37
Nested Sagas Syntax
(Step) X 0 A AB S (Process) P X
PP PP (Saga) S P
38
Nested Sagas Syntax
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Add Points
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S ? AORO UCRM POUS APSP
39
Nested Sagas Semantics
?
? ltP,0gt ?? lt , ßgt
?
(sub-cmt)
?
?
? ltP,ßgt ?? lt , ßßgt
ß acts as default compensation
?
? ltP,0gt ?? lt , 0gt
?
(sub-abt)
?
?
? ltP,ßgt ?? lt , ßgt
?
? ltP,0gt ?? lt , 0gt
?

(sub-fail)
?
? ltP,ßgt ?? lt , 0gt
?

40
Nested Sagas Semantics
(sub-forced-1)
(sub-forced-2)
(sub-forced-2)
41
Nested Sagas Adequacy
Completion
42
Nested Sagas Adequacy
Successful Compensation
43
Nested Sagas Adequacy
Failed Compensation
44
More on Sagas

• Exception handling try S with P
• Used to catch crashes during backward computation
• Forward recovery strategies try S or P
• Can be used to retry or to improve activities
• Fully programmable compensations SP
• More expressive than default compensation
  (sub-cmt)
• Allowed by languages like BPEL4WS
• Choices
• discriminator P?Q
• internal P?Q
• Data dependencies A?B
• Valid executions must satisfy dependency
  constraints

45
Final Remarks

• Our definition for compensable languages
• abstracts away from low-level computations
• can be easily extended
• independent from the coordination mechanisms that
  implement the primitives
• Java Transactional Web Services (JTWS)
• Distributed implementation of flows
• Allows to reason about program properties
• Adequacy
• Correctness of implementation