Stateful-WoT: Capturing the Behavior of Highly Dynamic Cyber-Physical Systems

By introducing the Web of Things (WoT) standard, W3C aims to provide a unified interface description format to counter the high fragmentation of the Internet of Things (loT) landscape. This description format, called the Thing Description (TD), is a static, JSON-Linked Data (JSON-LD) document that is both human and machine-readable. It lists all possible interactions of a Thing and any additional metadata needed to perform these interactions, abstracting away from the internal behavior of Things. As such, the static TD lacks a formal way of describing highly dynamic, physical Things and how the availability of specific interactions may depend on the current physical state of the Thing. In this work, we introduce Stateful-WoT, a method and an open-source implementation that facilitates the modeling of Things and their behavior using State Chart XML (SCXML) state machines and Modelica models. The resulting hybrid state chart is serializable and exchangeable, enabling the exchange of the state chart alongside the TD. Our proposed extension to SCXML allows us to fully model a Thing and its interface, facilitating the automatic generation of implementation code and reactive Digital Twins (DTs). We showcase the benefits and viability of our approach and implementation by modeling and generating the DT of two highly dynamic Things with high accuracy. Our proposal makes developing WoT applications more accessible, faster, and much more reliable for complex industrial scenarios.