Diapositiva 1

1
From Theory to Practice in Transactional
Composition of Web Services
University of Pisa
Roberto Bruni, Gianluigi Ferrari, Hernàn
Melgratti, Ugo Montanari, Emilio Tuosto
Daniele Strollo
2
Schedule

• Introduction to Sagas
• Basic concepts of JTWS
• Java Signal Core Layer (JSCL)
• Java Transactional Layer (JTL)
• Examples

3
Long Running Transactions

• Transactions in e-Business scenario
• ACID properties are relaxed
• atomicity (long running)
• isolation (concurrency).
• LRTs with compensation as solution to failures
• undo
• alternatives to restoring of state (e.g. refund
  money)

Plain Reservation Service
Reservation Request

• Payment Service
• bank account (atomicity)
• credit card (isolation)

Payment
Request for canceling reservation
4
Long Running Transactions

• Long-Running Transactions (LRTs)
• Independent components loosely coupled
• Each component maintains the consistency of its
  local data
• Illusion of Atomicity given by compensations
• Ad-hoc activities responsible for undoing the
  effects of partial executions when the whole
  computation cannot be completed.
• Current proposals lack from formal foundations
• Hard to prove properties

5
Our goal

• To provide a formally specified language for
  defining transactional aggregations at high level
  of abstraction.
• To map high level transactional primitives into
  concrete coordination patterns.

6
Saga Calculus (SC) syntax

• Atomic activities
• ? 0, THROW
• Ranged over by A, B,
• Processes
• P A B PP PP
• Sagas
• S A P SS SS

Saga Calculus naturally abstracts away from low
level computational details and communication
patterns BMM_at_POPL05. The formal semantics is
given by traces BHF_at_25YCCS,BBFHMM_at_CONCUR05.
7
Basic concepts of SC compensable process

• Compensable process
• P AB
• P executes the main activity A and installs the
  compensation activity B
• B is not installed if A is not completely
  executed
• A is called forward flow and B the backward flow

8
Basic concepts of SC Saga

• The process P contained in a Saga S
• S P
• Encloses the execution of process P in an atomic
  context.
• The execution of successful backward flow is
  isolated from the outside.
• Only in case of unsuccessful compensation action,
  the event is forwarded to previous stages.

9
Purchase orders
Update Credit
Accept Order
Prepare Order
10
Purchase orders without compensations
Update Credit
Accept Order
Prepare Order
S AO UC PO
The possible traces are ? S lt ,
, gtlt , , gt
AO
UC
PO
AO
UC
PO
11
Purchase orders with compensations
Update Credit
Refund Money
Accept Order
Refuse Order
Prepare Order
Update Stock
S AORO UCRM POUS
Successful execution ? S ltAO, UC, PO,
XgtltAO, PO, UC, Xgt Failure with successful
compensation (not enough money) ? S ltAO,
PO, US, RO, Xgt Failure and unsuccessful
compensation (unable to resemble stock) ? S
ltAO, PO, !gt
12
Schedule

• Introduction to Sagas
• Basic concepts of JTWS
• Java Signal Core Layer (JSCL)
• Java Transactional Layer (JTL)
• Examples

13
JTWS Architecture

• JSCL defines
• Async/sync signal passing
• Signal links
• Logical ports
• Handler/Emitter
• Generic Component
• management of flow sessions

• JTL defines
• Types of signals useful to represent LRTs
• Sequential and Parallel composition of services

14
Schedule

• Introduction to Sagas
• Basic concepts of JTWS
• Java Signal Core Layer (JSCL)
• Java Transactional Layer (JTL)
• Examples

15
JSCL application building blocks

• Logical Ports
• AND / OR / NOT

SIG_TRUE
SIG_TRUE
SIG_FALSE
SIG_FALSE
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Example
eventType1
eventTypen
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JSCL in detail

• Connecting two components
• The Emitter makes a request to a handler to be
  connected
• The Handler gives the permissions to the Emitter
  to create the input signal link

connectSignal
registerSignal
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JSCL in detail

• Connecting two components
• The Emitter makes a request to a handler to be
  connected
• The Handler gives the permissions to the Emitter
  to create the input signal link

• Forwarding a signal
• Emitter emitSignal (signal, async)
• Handler the method handleSignal (signal, async)
  is invoked automatically . This method
  propagates the signal to all the registered
  handlers.

The asynchronous signals are managed by the
handler.
emitSignal
handleSignal
Queue
19
Schedule

• Introduction to Sagas
• Basic concepts of JTWS
• Java Signal Core Layer (JSCL)
• Java Transactional Layer (JTL)
• Examples

20
JTWS Java Transactional Layer (JTL)

• Prefixed set of signals with a precise
  semantics
• SNG_INVOKE,
• SGN_COMMIT,
• SGN_ROLLBACK
• Structural composition of services
• Sequence and Parallel
• Well defined semantics for transactional flows.

JTL Component
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JTL AtomicTask

• AtomicTask defines the interface that each atomic
  activity of SC must fit.

• We assume that any class which implements
  AtomicTask cannot throw any exception but
  AtomicActionException.

22
JTL Basic Compensable Process

• A SC compensable process is defined in JTL as
• Comp (A, B) A B
• with A,B AtomicTasks.
• The forward flow corresponds to the execution of
  A.
• The backward flow corresponds to the the
  execution of B.
• Exceptions are raised in presence of faults
  during execution of B.

A
B
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JTL Basic Compensable Process...
A
Successful execution of A
Unsuccessful execution of A
Executes main activity A
B
Request for abort. Executes B.
Compensation successful executed
Compensation failure
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JTL sequence

• Seq (P, Q) PQ
• JTLSequence.addInternalComponent (JTLComponent)
  permits to add new components in the sequence.

In
Out
oCt
iCt
iRb
oRb
iEx
oEx
seq.addInternalComponent (Q)
25
JTL sequence
In
Out
A
oCt
iCt
iRb
oRb
iEx
oEx
26
JTL sequence
In
Out
A
oCt
iCt
B
iRb
oRb
iEx
oEx
27
JTL sequence
In
Out
oCt
iCt
B
iRb
oRb
iEx
oEx
28
JTL sequence
In
Out
oCt
iCt
B
iRb
oRb
iEx
oEx
29
JTL sequence
In
Out
oCt
iCt
B
iRb
oRb
iEx
oEx
30
JTL sequence
In
Out
oCt
iCt
iRb
oRb
iEx
oEx
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JTL parallel
Par (P, Q) PQ
Dispatcher
P
Q
Collector
Status (-,-)
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JTL parallel
Dispatcher
A
P
A
Q
Collector
Status (---,---)
33
JTL parallel
Dispatcher
A
P
A
Q
Collector
Status (Inv,---)
34
JTL parallel
Dispatcher
A
P
A
Q
Collector
Status (Inv,Inv)
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Saga in JTL

• The behavior of a Saga S P in JTL is the
  following
• If P sends an Inv signal
• S propagates internally the Cmt signal
• S sends externally the Inv signal
• If P sends an Rb signal
• S sends externally the Inv signal
• If P sends an Exc signal
• It is ignored since the status is inconsistent

36
JTL saga
In
Out
Exc and Cmt ignored while Abt is transformed to
Inv
SignalH
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Schedule

• Introduction to Sagas
• Basic concepts of JTWS
• Java Signal Core Layer (JSCL)
• Java Transactional Layer (JTL)
• Examples

38
Purchase Order in JTL
Update Credit
Refund Money
Accept Order
Refuse Order
Prepare Order
Update Stock
S AORO UCRM POUS
Seq ( Comp (AO, RO), Par ( Comp (UC, RM), Comp
(PO, US)))
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Purchase Order in JTL graphical representation
Out
In
Out
In
UC
RM
AO
RO
PO
iCt
oCt
iCt
oCt
iRb
oRb
US
iRb
oRb
iEx
oEx
iEx
oEx
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JTWS advantages

• JSCL
• Basic framework for programming coordination.
• Abstraction for communication details.
• Logical ports permit a simple design of the flow
  diagrams.
• The connections can be modified at run-time.
• Distributed flow execution.
• Primitives for authorizing access to signals.
• JTL
• Based on a robust theory
• Simple to program
• Extendible to other transactional logics

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Concluding remarks

• From a formal specification of naïve sagas we
  have presented JTWS.
• Contribution is a setting for designing business
  process transactions
• Visual/graphical representation of parallel sagas
• Process calculus description in bijective
  correspondence with sagas diagrams
• Executable, distributed translation of symbolic
  processes
• Future works
• GUI to develop JTL and JSCL components
• Debugger environment to test the behavior of the
  involved components
• Support for advanced features like nesting,
  speculative choice (N. Zappone).

42
oOOo lt(. .)gt oOOo

• ?

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Semantics of Saga Calculus.
COMPOSITION OF STANDARD TRACES
int(p,q) represents all the possible interleaving
of the observable flows p,q.
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Semantics of Saga Calculus..
TRACES OF Naive Sagas
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Semantics of Saga Calculus...
COMPOSITION OF COMPENSABLE TRACES
46
Semantics of Saga Calculus.
TRACES OF COMPENSABLE PROCESSES
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JSCL in detail

• Connecting two components
• The Emitter makes a request to a handler to be
  connected
• The Handler gives the permissions to the Emitter
  to create the input signal link

• Forwarding a signal
• Emitter emitSignal (signal, async)
• Handler the method handleSignal (signal, async)
  is invoked automatically . This method
  propagates the signal to all the registered
  handlers.

The asynchronous signals are managed by the
handler.