BPMN on Ethereum - ut BPMN%ENGINE%ON%ETHEREUM%%%%%LUCIANO%GARCÍA2BAÑUELOS% 12...

A lightweight BPMN Execution Engine on Ethereum Luciano García-‐Bañuelos

University of Tartu

Blockchain ...

BPMN ENGINE ON ETHEREUM LUCIANO GARCÍA-‐BAÑUELOS 8/11/16 1

Taken from hBp://smartmoney.startupitalia.eu/wp-‐content/uploads/sites/7/2016/03/catena-‐bitcoin.jpg

From the point of view of this talk • Distributed, highly (fully?) replicated, append only database

• Each record that is inserted into the database is secured from tampering and revision

• Keywords ◦ Distributed: The database is highly replicated, following a peer-‐to-‐peer architecture (there is not a central master node)

◦ Append-‐only storage: Wri_ng to the database can only happen by adding new records at the end of it

◦ Descentralized consensus: the majority of nodes needs to agree that a yet-‐to-‐be-‐added record is legi_mate or not

8/11/16 BPMN ENGINE ON ETHEREUM LUCIANO GARCÍA-‐BAÑUELOS 2

Bitcoin’s take on blockchain

Assume “Alice” sends some bitcoins to “Bob”, a bitcoin transac_on will accordingly store: •  An input: This is a record of which bitcoin address was used to send the bitcoins to “Alice” in the first place

•  An amount: The amount of bitcoins being traded

•  An output: This is “Bob”’s bitcoin address


Image taken from “Mastering Bitcoin” by Andreas M. Antonopoulos, O’Really

Ethereum’s take on blockchain


Image taken from hBps://blog.ethereum.org/wp-‐content/uploads/2015/11/ethblockchain_full.png

Ethereum components: 1)  A distributed blockchain (similar to Bitcoin) 2)  A compu_ng plahorm that enables the execu_on of Smart Contracts

The above is done on top of the Ethereum Virtual Machine (EVM)

Smart contract … • Programs living on the blockchain (e.g. Ethereum) with their own memory and code

• Blockchain transac_ons via execu_on of contract func_ons (clauses)

• Manipulate persistent data (contract state), transfer ether, interact with other contracts or with “agents”


Blockchain as a plaEorm for collaboraFve business processes • Par_cipants agree on a collabora_ve process and a model for it

• The model is translated to a smart contract(s) to be executed on the blockchain

• Smart contracts listen to process execu_on events and interact with agents or other smart contracts in order to monitor and/or execute the process


Blockchain as a plaEorm for collaboraFve business processes



• The model is translated to a smart contract(s) to be executed on the blockchain


6 Weber, Xu, Riveret, Governatori, Ponomarev, and Mendling

Translator

BPMN model

Design Time

Factory contract

Process implementation

Figure 2: Overview of our approach

3.2 Design Time: Translator

The translator is used at design time: it takes an existing business processspecification as input and generates smart contracts. These implement the C-Monitor or mediator and can be deployed and executed on the blockchain.

In a collaborative process, this functionality must be split and distributedbetween the smart contract and the triggers. The translator creates the artifactsin such a way that the triggers and the smart contract can collaborate directlywith each other over the blockchain network.

When the translator is called, it may not be known which participants willplay which roles. Therefore, the translator outputs only a factory contract,which in turn contains all information needed for instantiating the process. Thefactory contract includes the methods for instantiation and two types of artifacts:(i) an interface specification per role (e.g., buyer, manufacturer, and shipper) ina collaborative process, to be distributed to the respective triggers, and (ii) aprocess instance contract, which is deployed to the blockchain when the processis instantiated. The process instance contract contains the implementation of thebusiness logic and takes the form of a C-Monitor or mediator, depending on thecontent of the original process specification.

The overall translation algorithm has two phases. First, the translator parsesthe input process model and iterates through all its elements, where it generatestwo lists per element in the process model: one list of previous elements and oneof next elements. Then, the translator translates each element with its respectivelinks, generating Solidity code based on the translation rules for di↵erent typesof elements as detailed in the TR [23]. Note that, in the current implementation,only some combinations of consecutive gateways can be connected to each otherwithout tasks in between. The previous element list is used by the translator todetermine which other elements need to be deactivated when the current element


• Smart contracts listen to process execu_on events and interact with agents or other smart contracts in order to monitor and/or execute the process


6 Weber, Xu, Riveret, Governatori, Ponomarev, and Mendling

Run Time

On blockchain

Off blockchain

Internal process

Interface

Internal process

Interface

Internal process

Interface

Data payload

Data payload

Data payload

Key distributor

Trigger

Factory contract

Process instance contract ( Mediator / Monitor )

Escrow

Verification

Deposit collector

Execution state

Partial data payload

Participants account

Business logic ( Active / passive )

Trigger Trigger

Figure 2: Overview of our approach

3.2 Design Time: Translator

The translator is used at design time: it takes an existing business processspecification as input and generates smart contracts. These implement the C-Monitor or mediator and can be deployed and executed on the blockchain.

In a collaborative process, this functionality must be split and distributedbetween the smart contract and the triggers. The translator creates the artifactsin such a way that the triggers and the smart contract can collaborate directlywith each other over the blockchain network.

When the translator is called, it may not be known which participants willplay which roles. Therefore, the translator outputs only a factory contract,which in turn contains all information needed for instantiating the process. Thefactory contract includes the methods for instantiation and two types of artifacts:(i) an interface specification per role (e.g., buyer, manufacturer, and shipper) ina collaborative process, to be distributed to the respective triggers, and (ii) aprocess instance contract, which is deployed to the blockchain when the processis instantiated. The process instance contract contains the implementation of thebusiness logic and takes the form of a C-Monitor or mediator, depending on thecontent of the original process specification.

The overall translation algorithm has two phases. First, the translator parsesthe input process model and iterates through all its elements, where it generatestwo lists per element in the process model: one list of previous elements and oneof next elements. Then, the translator translates each element with its respectivelinks, generating Solidity code based on the translation rules for di↵erent typesof elements as detailed in the TR [23]. Note that, in the current implementation,only some combinations of consecutive gateways can be connected to each otherwithout tasks in between. The previous element list is used by the translator todetermine which other elements need to be deactivated when the current element

Smart contract ... • Described by Nick Szabo in the late 90s

The basic idea behind smart contracts is that many kind of contractual clauses (e.g. collaterals, bonding, delinea_on of property rights) can be embedded in hardware and solware in such a way as to make breach of contract expensive for the breacher


Smart contract? • Contract: Tradi_onal way to formalize a rela_onship

• Defini_on from Merriam-‐Webster ◦ A binding agreement between two or more persons or par_es, especially one legally enforceable

◦ A business arrangement for the supply of goods or services at a fixed price

◦ The act of marriage or an agreement to marry

◦ A document describing the terms of a contract


A concrete example … • Within a limited amount of poten_al loss, the vending machine takes in coins and dispenses change and product according to the displayed price

• Vending machine implements a sort of contract with bearer: ◦ Anybody with coins can par_cipate

◦  Some security mechanisms protect stored coins and product from aBackers


By Minnesota Historical Society -‐ Original Image taken from The Minnesota Historical Society on Flickr, CC BY-‐SA 2.0, hBps://commons.wikimedia.org/w/index.php?curid=6608597

Another example: Remote purchase


BPMN view of the process


Escrow (S

mart contract)

Purchase contractcreated

Notify Buyer about contract

creation

Confirm purchase (payment)

Notify Seller about payment

Confirm reception

Notify Seller about reception

Buyer

Seller

Remote purchase - Choreography

Create purchase contract

Seller

Buyer

Confirm purchase(payment)

Seller

Buyer

Ship product

Seller

Shipping company

Confirm reception

Seller

Buyer

Purchase details

Payment details

Shipment details

Delivery details

Deliver product

Shipping company

Buyer

Another example: Remote purchase


Remote purchase (cont)


Remote purchase … middleman


Escrow

Smart contract on BPMN


Escrow (S

mart contract)

Purchase contractcreated

Block Seller deposit

Notify Buyer about contract

creation

Notify Seller about payment

Confirm purchase

Confirm reception

Transfer payment to Seller and

unblock Seller's deposit

Block buyer's payment and

depositPurchase completed

Notify Seller about reception

Unblock Buyer's deposit

Cancel transaction

Unblock Seller'sdeposit

Purchase cancelled by

Seller

Seller

Buyer

Demo Fme


Temporal constraints on BPMN


Cancellation by guest

Cancellation by host

Block host & guest deposit

7 days before checkin

BPMN on Ethereum - ut BPMN%ENGINE%ON%ETHEREUM%%%%%LUCIANO%GARCÍA2BAÑUELOS% 12...

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