System-wide IoT design and programming: Patterns for decentralised collective processes

The Internet of Things promotes a view of large-scale deployments of devices able to compute, communicate, and interact with their surrounding environment. In this context, one significant challenge revolves around designing and programming collective processes, i.e., durable activities involving the collaboration of large groups of devices. Examples of collective processes include distributed sensing, collective decision-making, collective movement/transport, and adaptive maintenance of system-level structures. To address the issues involved in developing such kinds of system-wide behaviours, research has proposed multiple approaches, abstractions, and algorithmic solutions. In particular, the approach of aggregate processes has emerged as a promising formal technique for programming collective processes by a macro-level perspective while supporting decentralisation, abstraction, and resilience. In order to characterise (i) previous work on aggregate processes, (ii) the usages and applications that this technique may foster, and (iii) draw general design insights in the realm of collective computing, this article provides a characterisation of common problems and solutions based on aggregate processes. What results is a catalogue of design patterns for decentralised collective processes. Specifically, we provide a taxonomy of patterns, describe each pattern in a schematic form, and discuss the implications for the design of collective processes for the Internet of Things and related scenarios.