CATERPILLAR: A Business Process Execution Engine on the Ethereum Blockchain (1808.03517v3)

Abstract: Blockchain platforms, such as Ethereum, allow a set of actors to maintain a ledger of transactions without relying on a central authority and to deploy scripts, called smart contracts, that are executed whenever certain transactions occur. These features can be used as basic building blocks for executing collaborative business processes between mutually untrusting parties. However, implementing business processes using the low-level primitives provided by blockchain platforms is cumbersome and error-prone. In contrast, established business process management systems, such as those based on the standard Business Process Model and Notation (BPMN), provide convenient abstractions for rapid development of process-oriented applications. This article demonstrates how to combine the advantages of a business process management system with those of a blockchain platform. The article introduces a blockchain-based BPMN execution engine, namely Caterpillar. Like any BPMN execution engine, Caterpillar supports the creation of instances of a process model and allows users to monitor the state of process instances and to execute tasks thereof. The specificity of Caterpillar is that the state of each process instance is maintained on the (Ethereum) blockchain and the workflow routing is performed by smart contracts generated by a BPMN-to-Solidity compiler. The Caterpillar compiler supports a large array of BPMN constructs, including subprocesses, multi-instances activities and event handlers. The paper describes the architecture of Caterpillar, and the interfaces it provides to support the monitoring of process instances, the allocation and execution of work items, and the execution of service tasks.

• The paper introduces Caterpillar, an engine integrating business process management capabilities with Ethereum for decentralized and compliant process execution.
• Caterpillar enforces execution compliance by design using on-chain smart contracts for workflow logic and off-chain components for model compilation and monitoring.
• The evaluation shows Caterpillar achieves high integrity in process enforcement on Ethereum, trading higher computational cost for enhanced security and decentralized execution.

Caterpillar: A Business Process Execution Engine on the Ethereum Blockchain

This paper introduces Caterpillar, a sophisticated business process execution engine developed specifically for deploying and running process-centric applications on the Ethereum Blockchain. Traditional business process management systems (BPMSs) provide abstractions for the efficient development of business processes but do not inherently offer decentralized control or transparent, immutable features inherent to blockchain platforms. Caterpillar addresses this gap by synthesizing BPMS capabilities with blockchain technology, propelling the execution of collaborative processes where mutual distrust exists among the parties involved.

Caterpillar is designed to support execution compliance by design, ensuring that parties involved in the process cannot perform operations that stray from the agreed-upon process model encoded as smart contracts. To achieve this, Caterpillar introduces several architectural layers and functionalities that differentiate it from traditional BPMSs:

• On-chain Runtime and Storage: This layer involves smart contracts for workflow handling, worklist management, and service bridging. It maintains the control-flow logic and execution state entirely on the blockchain. A log externalizes events for interaction with off-chain components.
• Off-chain Runtime: Comprising the BPMN compiler, deployment mediator, execution monitor, and event monitor, this layer facilitates the compilation of BPMN models into smart contracts, deployment, execution monitoring, and communication between blockchain and external systems. These off-chain components can operate independently per actor involved and ensure blockchain integrity even if tampered.
• Web Portal: Enabling interaction through a visual interface, this portal facilitates task execution, process monitoring, and model authoring, advancing user engagement and responsiveness.

Noteworthy is the sophisticated handling of BPMN constructs, including subprocesses, boundary events, and multi-instance activities. These elements are pivotal for executing complex and nested business logic within subdivided operational steps, ensuring robust process enforcement and flexibility.

For practical implementation, Caterpillar involves converting BPMN models into Solidity contracts. This involves managing interactions and state transitions using Ethereum's distributed ledger capabilities, effectively encoding business logic into immutable smart contracts executed across decentralized nodes.

The evaluation of Caterpillar demonstrates its ability to enforce business processes with significant integrity, albeit at a higher computational cost compared to traditional methods that utilize blockchain only for logging or simplified process monitoring. This tradeoff is balanced by increased security and the fulfiLLMent of decentralized process execution capabilities.

Looking forward, enhancing Caterpillar to include dynamic role binding and sophisticated access control tailored to inter-organizational process scenarios represents a strategic future direction. Additionally, examining its performance across different blokchain configurations, including consortium blockchains that offer higher throughput, remains essential for high-volume process models prevalent in industry settings.

Caterpillar not only advances academic discourse around blockchain-integrated BPM systems but also pioneers practical pathways for businesses migrating towards decentralized process management solutions. Through its integration of BPMN with blockchain, Caterpillar is poised to underlie future decentralized applications involving complex collaborative business processes.