Many research works apply blockchain technologies to several different application domains ranging from supply chain and logistics to healthcare and real-estate. There, nevertheless, the blockchain performs the same two core tasks: identity management and asset tracking. In this paper we analyse how the blockchain can be exploited beyond these traditional tasks, towards coordination of distributed processes. To this end, we design and develop proof-of-concept implementations of the Linda model on top of different blockchains, and compare their strengths and shortcomings.

1. Comparative Analysis of Blockchain Technologies
under a Coordination Perspective
Giovanni Ciatto1 Michael Bosello1 Stefano Mariani2
Andrea Omicini1
giovanni.ciatto@unibo.it michael.bosello@studio.unibo.it
stefano.mariani@unimore.it andrea.omicini@unibo.it
1Dipartimento di Informatica – Scienza e Ingegneria—Universit`a di Bologna
2Dipartimento di Scienze e Metodi dell’Ingegneria, Universit`a di Modena e Reggio Emilia
2nd International Workshop on
BlockChain Technologies 4 Multi-Agent Systems
´Avila, Spain – June 27, 2019
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 1 / 24

2. Outline
1 What & Why
2 Ok, How?
3 Comparison
4 Cool, Then?
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 2 / 24

3. What & Why
Next in Line. . .
1 What & Why
Coordination
2 Ok, How?
Linda as a test-bed
3 Comparison
Ethereum
HyperLedger Fabric (HLF)
Corda
4 Cool, Then?
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 3 / 24

4. What & Why
Premises
a lot of BCT have been developed in the recent years
some are simply aimed at improving crypto-currencies
other are conceived to be general and track custom assets
through some sort of programmability
e.g. by means of smart contracts
Some foundational question arise
can BCT be used to mediate the interaction of
off-chain entities?
on-chain entities?
can it be used for coordination?
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 4 / 24

5. What & Why
Premises
a lot of BCT have been developed in the recent years
some are simply aimed at improving crypto-currencies
other are conceived to be general and track custom assets
through some sort of programmability
e.g. by means of smart contracts
Some foundational question arise
can BCT be used to mediate the interaction of
off-chain entities?
on-chain entities?
can it be used for coordination?
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 4 / 24

6. What & Why Coordination
What is Coordination?
Within MAS
“A framework in which the interaction of active and independent entities
called agents can be expressed” [Cia96]
active entities i.e., proactive, computationally autonomous
interaction dependencies among agents activities
e.g. communication, cooperation, competition, etc.
expressed i.e., explicitly represented, or observed
Takeaway
Coordination studies interaction at the fundamental level
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 5 / 24

7. What & Why Coordination
Wait: but why Coordination & BCT?
BCT provide highly-desirable properties
ordering of events
consistency among replicated data
accountability of actions
identity management
(byzantine) fault tolerance
Especially in MAS!
Accountable, trusted communications, and consistency of information are
long-standing issues for open MAS [RHJ04, HM15]
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 6 / 24

8. Ok, How?
Next in Line. . .
1 What & Why
Coordination
2 Ok, How?
Linda as a test-bed
3 Comparison
Ethereum
HyperLedger Fabric (HLF)
Corda
4 Cool, Then?
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 7 / 24

9. Ok, How? Linda as a test-bed
Our test-bed – Tuple-based coordination in Linda I
Linda at a glance
Archetypal tuple-based coordination model [Gel85]
4 main elements
tuples — structured data chunks
templates — pattern language for tuples
tuple spaces — blackboards for tuples
primitives — put (out), or access, i.e. read (Rd), or consume (In)
3 main features
generative — tuples independent from agents
associative — tuples accessed through templates; no addr. & no ref.
suspensive — access attempts suspended if no tuple is available
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 8 / 24

10. Ok, How? Linda as a test-bed
Our test-bed – Tuple-based coordination in Linda II
Useful in MAS?
TL;DR Yes! [OZKT01]
Linda over BCT
How can primitives be implemented on BCT?
Can we reproduce suspendive semantics?
Does it work for
off-chain agents?
on-chain agents?
Are there differences among BCT w.r.t. interaction?
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 9 / 24

11. Ok, How? Linda as a test-bed
Comparison Dimensions for BCT
openness — whether they are permissioned or permissionless
access control — degrees of freedom in controlling access to assets
architecture — main roles for nodes composing the BCT network
state model — how (i.e., in which form) the BCT tracks information
asset — which sort of assets may be manipulated by users
programmability — how the programmable elements are called
meta-primitives — how programmable elements can be manipulated
primitives — operations letting programmable elements interact
consensus — how the BCT supports consistency
termination — how BCT prevent infinite computations
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 10 / 24

12. Comparison
Next in Line. . .
1 What & Why
Coordination
2 Ok, How?
Linda as a test-bed
3 Comparison
Ethereum
HyperLedger Fabric (HLF)
Corda
4 Cool, Then?
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 11 / 24

13. Comparison Ethereum
Ethereum at a Glance
openness → permissionless
access control → none
architecture → light nodes (clients) + full nodes (miners)
state model → accounts
asset → byte strings
programmability → smart contracts (SC)
meta-primitives → Deploy, Call
primitives → Call (inter-SC), Raise Event (SC-to-client)
consensus → Proof of Work (all miners)
termination → gas
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 12 / 24

14. Comparison Ethereum
Linda over Ethereum
Details ! more in [CMO18]
tuple spaces → smart contracts
coordinated agents → clients
primitives → method calls through the Call meta-primitive
suspensive semantics → listening for events
Peculiarities
economy of coordination [CMO18]
Shortcomings
smart contracts cannot be coordinated agents
no concurrency for primitives
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 13 / 24

15. Comparison HyperLedger Fabric (HLF)
HyperLedger Fabric (HLF) at a glance
openness → permissioned
access control → Membership service, Channels, Endorsement policies
architecture → peers + endorsement peers + ordering nodes
state model → Key-Version-Value (KVV) triplets
asset → KVV triplets
programmability → chaincodes (C)
meta-primitives → Deploy, Invoke, Query
primitives → Invoke (inter-C), SetEvent (C-to-peer)
consensus → pluggable (default: PBFT [CL02])
termination → execute-order-validate architecture [ABB+18]
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 14 / 24

16. Comparison HyperLedger Fabric (HLF)
Linda over HLF
Details
tuple spaces → chaincodes
coordinated agents → peers
primitives → method calls through the Invoke meta-primitive
suspensive semantics → listening for events
Peculiarities
finer control w.r.t. replication, consensus, tuple space access
some degree of concurrency w.r.t. primitives
Shortcomings
smart contracts cannot be coordinated agents
workaround needed for completing multiple primitives at once
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 15 / 24

17. Comparison Corda
Corda at a Glance
openness → permissioned
access control → Doorman service + Flows
architecture → nodes + notary services (notaries)
state model → unspent transaction output (UTXO) + Vaults
asset → states
programmability → contracts
meta-primitives → none (contracts deployed by admins)
primitives → none (validation only)
consensus → pluggable (custom algorithm)
termination → not a problem (contracts are trusted)
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 16 / 24

18. Comparison Corda
Linda over Corda
Details
tuple spaces → vaults
coordinated agents → nodes
primitives → state creation, or consumption
suspensive semantics → flows
Peculiarities
subjective visibility of tuples in tuple spaces
some degree of concurrency w.r.t. primitives
Shortcomings
! tight coupling among coordinated agents
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 17 / 24

19. Cool, Then?
Next in Line. . .
1 What & Why
Coordination
2 Ok, How?
Linda as a test-bed
3 Comparison
Ethereum
HyperLedger Fabric (HLF)
Corda
4 Cool, Then?
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 18 / 24

20. Cool, Then?
Takeaways
The good
BCT can in general be used for coordination off-chain
permissioned BCT allow for a finer control w.r.t. tuple visibility to
off-chain entities
What can be improved
on-chain computational entities may benefit coordination as well
because they can be conceived as agents [CMMO19]
even if this is currently poorly understood by the community
The bad
Linda-based coordination is not fully supported by Corda
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 19 / 24

21. Conclusions and Future Work
Conclusion
Summarising, we
compared three programmable BCT, namely Ethereum, HLF, & Corda
w.r.t. the coordination perspective, by implementing Linda on them
thus testing capabilities, peculiarities, and limits of BCT
and showing that smart contracts fall short w.r.t. mutual interaction
In the future, we plan to
extend our comparison to more technologies
propose a novel programmable BCT overcoming current limitations
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 20 / 24

22. Conclusions and Future Work
Conclusion
Summarising, we
compared three programmable BCT, namely Ethereum, HLF, & Corda
w.r.t. the coordination perspective, by implementing Linda on them
thus testing capabilities, peculiarities, and limits of BCT
and showing that smart contracts fall short w.r.t. mutual interaction
In the future, we plan to
extend our comparison to more technologies
propose a novel programmable BCT overcoming current limitations
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 20 / 24

23. Comparative Analysis of Blockchain Technologies
under a Coordination Perspective
Giovanni Ciatto1 Michael Bosello1 Stefano Mariani2
Andrea Omicini1
giovanni.ciatto@unibo.it michael.bosello@studio.unibo.it
stefano.mariani@unimore.it andrea.omicini@unibo.it
1Dipartimento di Informatica – Scienza e Ingegneria—Universit`a di Bologna
2Dipartimento di Scienze e Metodi dell’Ingegneria, Universit`a di Modena e Reggio Emilia
2nd International Workshop on
BlockChain Technologies 4 Multi-Agent Systems
´Avila, Spain – June 27, 2019
Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 21 / 24

24. References
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Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 22 / 24

25. References
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26. References
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Ciatto et al. (UniBo, UniMoRe) Comparative Analysis of BCT BCT4MAS 2019, June. 26 24 / 24