Abstract
The Web of Things (WoT) paradigm enables access to physical world things and their data through standard Web protocols. This provides interoperability at the hardware and communication protocol level, but does not add intelligence to the things or facilitate unambiguous interpretation of their data. The evolution of the WoT towards the semantic WoT offers the promise of meeting the interoperability challenge through the use of semantic Web technologies. The W3C Web of Things initiative encourages the use of common vocabularies to ensure interoperability and a common understanding of the domain knowledge. Ontologies provide a structured, common formalism to the disparate elements of the WoT and can form the basis of a common knowledge base. The research community and standardisation bodies have developed numerous ontologies describing the elements of the WoT and associated domains. A comprehensive review of the various proposed ontologies is needed to facilitate the adoption and reuse of the available models. This survey reviews the current state-of-the-art in WoT ontologies, which are presented from two perspectives: cross-domain ontologies which are classified into device, service, data and localisation models, and domain ontologies, which are presented from an environmental and user-oriented perspective.