Web of Things System Description for Representation of Mashups

The World Wide Web Consortium (W3C) created the foundations for widespread interoperability in the Internet of Things (IoT) with the publication of the Thing Description (TD) standard in the context of the Web of Things (WoT). TDs allow to interact with new as well as existing IoT devices by describing their network-facing interfaces and how to interact with them in a standardized way that is both human-and machine-readable. An important question that is left in this domain is how to create, represent and share systems of IoT devices, called Mashups. The techniques introduced in this paper improve the management of such Mashups. We propose two representations for such systems that both have unique advantages and are capable of representing interactions with Things, combined with application logic: A subset of the Unified Modeling Language Sequence Diagram presentation, referred to as WoT Sequence Diagram, and a TD that is enhanced with additional keywordobject pairs, referred to as WoT System Description. For the latter, we present an algorithm to automatically generate code that can be deployed to a device, making it act as a Mashup controller. By stating their syntactical and semantical foundations, we show how each representation is defined and how it can be validated. Furthermore, we systematically show that both representations can be used interchangeably in the context of representing WoT Mashups and demonstrate this with conversion algorithms. We also make the definitions and validation methods for the proposed representations, the reference implementations of the mentioned algorithms and our evaluation publicly available. Our contribution thus allows safer system composition for WoT and enables a systematic approach to build WoT Mashups.