Formal Models for Distributed Negotiations Committed Join Calculus

1
Formal Models forDistributed NegotiationsCommitt
ed Join Calculus
XVII Escuela de Ciencias Informaticas (ECI 2003),
Buenos Aires, July 21-26 2003
Roberto Bruni Dipartimento di Informatica
Università di Pisa
2
Our Focus

• In commercial applications, separately designed
  and implemented components must interact
• commit (intermediate) results of long-running
  activities upon (partial) agreements
• e.g. e-commerce, on-line auction systems
• Formal models should
• avoid ad-hoc proprietary solutions
• offer alternatives to centralized transaction
  managers
• hide the coordination layer (separation of
  concerns)

3
Distributed Agreements

• Negotiations / Contracts
• commit, abort, compensation
• hierarchical decisions
• dynamic membership
• fully distributed control
• Process cooperation
• coordination / orchestration / choreography
• different platforms and policies
• Data integration
• unstructured documents in different formats

4
Prerequisites forModeling Contracts

• Local and global resources
• Local sub-contracts and decisions
• Global results posted upon commit
• Abort of ongoing contracts
• All participants must be informed
• Compensations can be activated
• Either abort or commit (no divergence)
• Dynamic joining of participants
• Contracts can be merged
• Nested structure of contracts

5
Commitment

• We have seen different concepts in different
  areas
• DataBase transactions
• Transactional Workflows
• Transition synchronization
• PDLs with commit primitives
• Committed choice languages

6
PDLs with commit

• Transactions in JavaSpaces and Linda
• create(x) and commit(x) prefixes
• event notification
• TraLinda
• typed messages (L / H) and atomic prefixing
• Long running transactions
• MINI-XLANG
• asynchronous ?-calculus with transactional
  context context(P,Pf,Pc)

7
Committed Choice Languages

• Logic programming
• Non determinism means exhaustive search of
  successful computations
• dont know non-determinism
• results are produced at the end
• Concurrent logic / constraint languages
• limit backtracking to improve efficiency
• dont care non-determinism (indeterminism)
• partial outputs during computation

8
Guarded Horn Clauses

• Head ? Guard Body
• Reduce Head to Body if Guard succeeds
• dont know when evaluating guards
• dont care when selecting clauses whose guards
  are true
• Flat guards
• conjunction of primitive predicates
• Deep guards (e.g. AKL)
• both primitive and programmed predicates

9
Our Proposal

• committed JOIN
• PDL presentation
• Non ACID
• Multiway
• Open Nesting
• Flexible
• Split / Join
• Programmable commit / abort / compensation
• Concurrency and distribution
• Distributed 2PC
• Different levels of abstraction

10
Why an extension of JOIN

• Well-known asynchronous calculus
• Distributed implementations
• Jocaml
• Polyphonic C
• Analogous to dynamic coloured Petri nets
• Running D2PC implementation
• CHAM semantics
• molecules form solutions enclosed in membranes
• nesting is free (via membranes)
• Typed serializability

Ongoing Work!
11
Committed JOIN Syntax
messages

• M,N 0 x?y? MN
• P,Q M def D in P PQ abort PQ
• D,E J?P D?E J?P
• J,K x?y? JK

programmable abort
merge definitions (boards) defined boards must
be disjoint from ordinary defined names
12
Committed JOIN Semantics
13
Committed JOIN Semantics
compensation is kept frozen
contract P can evolve in isolation
14
Committed JOIN Semantics
commit
global resources
15
Committed JOIN Semantics
compensation on abort
16
Committed JOIN Semantics
merge n ongoing contracts
17
JOIN vs cJOIN

• PROPOSITION
• cJOIN is a conservative extension of JOIN

P ?J Q iff P ?cJ Q (for P and Q JOIN processes)
18
A Multi-Way Contract
19
Multi-Level Nesting
20
Nested Abort
21
Nested Abort II
22
Hotel Booking
H ? def WaitBooking ? def
request?o? ? o?? price?? ? price??
confirm?v? ? BookedRoom?v? ?
price?? ? abort in offeringRoom
?request,confirm? Q ? BookedRoom?v?
? in WaitBooking

23
Hotel Booking
H ? def WaitBooking ? def
request?o? ? o?? price?? ? price??
confirm?v? ? BookedRoom?v? ?
price?? ? abort in offeringRoom
?request,confirm? Q ? BookedRoom?v?
? in WaitBooking C ? def
BookingHotel ? def hotelMsg ?r,c? ? def offer??
? c?visa? HotelFound ? offer?? ?
abort in r?offer? in searchRoom
?hotelMsg? Q in BookingHotel
24
Hotel Booking
H ? def WaitBooking ? def
request?o? ? o?? price?? ? price??
confirm?v? ? BookedRoom?v? ?
price?? ? abort in offeringRoom
?request,confirm? Q ? BookedRoom?v?
? in WaitBooking C ? def
BookingHotel ? def hotelMsg ?r,c? ? def offer??
? c?visa? HotelFound ? offer?? ?
abort in r?offer? in searchRoom
?hotelMsg? Q in BookingHotel
HB ? def searchRoom?hm? offeringRoom ?r,c? ?
hm?r,c? in H C
25
Hotel Booking
, WaitBooking , BookingHotel ? ? , ,
offeringRoom?request,confirm? Q , ,
searchRoom?hotelMsg? Q ? , ,
hotelMsg?request,confirm? Q Q ? , ,
request?offer? Q Q ? , , offer??,
price?? Q Q ? , , confirm?visa?,
HotelFound , price?? Q Q ? , ,
BookedRoom?visa?, HotelFound Q Q ? ,
BookedRoom?visa?, HotelFound
26
Trip Booking I
H as before F ? def WaitBooking ? def
request?o? ? o?? price?? ?
price?? confirm?v? ? BookedFlight?v? ?
price?? ? abort in
offeringFlight ?request,confirm? Q ?
BookedFlight?v? ? in WaitBooking

local name, different from homonym name in H
27
Trip Booking II
both needed to commit
C ? def hotelOK?fc? flightOK?hc? ? fc hc
? BookingHotel ? def hotelMsg?r,c? ? def
offer?? ? c?visa? hotelOK?flightConf?
? offer?? ? abort ? flightConf ?
HotelFound in r?offer? in searchRoom
?hotelMsg? Q ? BookingFlight ? def
flightlMsg?r,c? ? def offer?? ? c?visa?
flightOK?hotelConf? ? offer?? ? abort
? hotelConf ? FlightFound in
r?offer? in searchFlight ?flightMsg? Q
in BookingHotel BookingFlight TB ?
def searchRoom?hm? offeringRoom ?r,c? ?
hm?r,c? ? searchFlight?fm?
offeringFlight ?r,c? ? fm?r,c? in H
F C
28
Matching the Prerequisites

• Local and global resources
• Local sub-contracts and decisions
• Global results posted upon commit
• Abort of ongoing contracts
• All participants must be informed
• Compensations can be activated
• Either abort or commit (no divergence)
• Dynamic joining of participants
• Contracts can be merged
• Nested structure of contracts

29
ZS nets, JOIN and cJOIN

• ZS nets can be encoded in JOIN by attaching the
  dynamic creation of a local DTC to transitions
• Implementation of D2PC (transparent to users)
• Tokens must carry several channel names
• Each firing must undergo local DTCs approval
• cJOIN primitives allow a straightforward encoding
• No further protocol is needed
• Tokens carry just one contract identifier
• Firings directly correspond to reactions

30
ZS nets in JOIN
We encode basic nets, which are expressive enough
given a net (T,S) we define an agent def T
in S , where
E open e E ? def D in e(put,
lock ) state( E ) e calc e
e(p, L) ? e(p, L) e fork e, e
e(p, L) ? def D in e(p, L ? lock )
e(put, L ? lock ) state( ? ) e, e
join e e(p, L) e(p, L) ? e(p,
L ? L) p(L ? L, ? ) e close E
e(p, L) ? p(L, E )
default compensation
31
DTC in JOIN
the definition D is the following
state(H) put(L, F) ? commit(L \ lock , L ,
lock , F, H ) state(H) ? failed()
release(H) commit( l ? L, L, L, F, H) ?
commit(L, L, L , F, H) l(L, lock,
fail ) commit(L, L, L, F, H) lock(L, l, f
) ? commit(L ? (L \ L), L ? L, L ?
l , F, H ) commit(?, L, L, F, H) ?
release(F) commit(L, L, L, F, H) fail() ?
failed() release(H) failed() put(L, F) ?
failed() failed() lock(L, l, f) ? failed()
f() failed() fail() ? failed()
32
ZS nets in cJOIN
We encode basic nets, which are expressive enough
given a net (T,S) we define an agent def T
in S , where
E open e E ? def z?0 in e?z?
E e calc e e?z? ? e?z? e
fork e, e e?z? ? e?z? e?z?
e, e join e e?z? e?z? ? e?z?
e close E e ?z? ? E
dummy definition (JOIN way of declaring a local
id)
z and z have now identical scope and meaning
33
Committed Join Features

• Negotiations can be defined in terms of
  concurrent sub-negotiations
• Cooperation between contracts are given by
  merging definitions
• Global resources produced inside a negotiation
  are made available at commit time
• Commit means termination
• Explicit abort and compensation

34
Some results on cJoin

• cJoin is a conservative extension of Join
• P ?J Q iff P ?cJ Q. (P and Q Join processes)
• Zero-safe nets can be encoded as cJoin processes
• N(T,S) a ZS net. (S,?) ? (S,?) iff def T in
  S ? def T in S

35
cJOIN and Logic Languages

• Commit primitives of cJoin can be used to
  implement committed choices of AKL
• explicit encoding of search strategies and
  unification via continuation passing and
  compensation

36
Serializability

• A simple type system that guarantees
  serializability
• Shallow processes
• the start of a sub-negotiation can be postponed
  until all the cooperating sub-negotiations needed
  to commit can be generated inside its parent
  negotiation
• Proof via correspondence w.r.t. big step semantics

37
Encoding of cJOIN in JOIN

• Aim
• Define an implementation of cJOIN in JOIN
• Associate to every cJOIN process a JOIN process
  that simulate its behavior
• Ideas
• Identification of basic forms for definitions
• Definition of a type system to single out
  canonical processes
• Reuse controllers of the D2PC protocol

38
Abstract Semantics

• Expected Result
• Define the abstract representative of a cJOIN
  process
• a JOIN process describing all the stable
  behaviors of the original process

def a?x?b?y? ? def c?z? ? b?z? in a?y?
c?x? a?x?b?y? in a?1?b?2?
def a?x? b?y? ? a?y? b?x? in a?1?b?2?
39
Comparatives studies

• Comparison with other approaches for modeling
  long-running activities
• Transactional context of MINI-XLANG
• distinguish two kinds of compensations
• Goals
• Find limitations / restrictions
• Show the encoding of other common constructors
  (such as those in WMS)

40
References

• Committed actions for mobile calculi (PhD Thesis
  Proposal, Manuscript, 2003)
• H. Melgratti
• Nested commits for mobile calculi extending Join
  (Manuscript)
• R. Bruni, H. Melgratti, U. Montanari