Abstract
First come, first served: Critical choices between alternative actions are often made based on events external to an organization, and reacting promptly to their occurrence can be a major advantage over the competition. In Business Process Management (BPM), such deferred choices can be expressed in process models, and they are an important aspect of process engines. Blockchain-based process execution approaches are no exception to this, but are severely limited by the inherent properties of the platform: The isolated environment prevents direct access to external entities and data, and the non-continual runtime based entirely on atomic transactions impedes the monitoring and detection of events. In this paper we provide an in-depth examination of the semantics of deferred choice, and transfer them to environments such as the blockchain. We introduce and compare several oracle architectures able to satisfy certain requirements, and show that they can be implemented using state-of-the-art blockchain technology.
Highlights
A service failing due to a low-level system malfunction, an order from a customer being received, or a stock reaching the strike price—events are pervasive on every layer of abstraction in Business Process Management (BPM) (Weske, 2019), and reacting to them promptly significantly impacts the performance of an organization
An associated simulation timeline was chosen such that the events occur sequentially in order; that is, a transaction is sent for explicit events, a deadline is passed for timer events, or a condition on an oracle becomes true for conditional events
Due to the platform’s storage limitations, some approaches might not be feasible for all data sources and scenarios depending on the number of data updates: We have shown that on-chain history oracles might quickly become infeasible when the exponential pricing of storage in Ethereum fully comes into play
Summary
A service failing due to a low-level system malfunction, an order from a customer being received, or a stock reaching the strike price—events are pervasive on every layer of abstraction in Business Process Management (BPM) (Weske, 2019), and reacting to them promptly significantly impacts the performance of an organization. An important pattern in this context is deferred choice, which describes situations in which an exclusive branching decision in a process instance depends on which one of a set of events occurs first (Russell et al, 2006). For instance, a business process describing the purchase and usage of a train ticket, shown in Figure 1 as a Business Process Model and Notation (BPMN) collaboration diagram. The customer books a ticket, optionally using their subscription-based discount card, and takes the train as expressed by the message event et triggered by the Railway Infrastructure Manager (RIM). There are several alternative paths after the event-based gateway g—the canonical representation of deferred choice in BPMN (OMG, 2013). The customer may cancel their ticket (ec), severe weather may prohibit the train’s departure (ew), or the customer’s discount card may expire (ed).
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