Semantic Interoperability on the Internet of Things: The Semantic Smart Gateway Framework

Introduction

Internet of Things enables a global connectivity between the real world and a virtual world of millions of distributed entities (observed subjects / objects, sensing / actuating / identity / embedded devices, software applications / services), connects things, not only places or people, and brings real-time machine-published big data to the users of the existing Web.

The ‘things’ on the IoT are various physical entities that are of some interest to humans, e.g. a heater to control, a package to track, an industrial machine to monitor, the air temperature in a room to measure, the motion in a room to detect. Depending on the nature of these ‘things’, different technologies for connecting them to the IoT are used: a) identity devices (e.g. RFID tags or barcodes), b) sensing and actuating devices (e.g. temperature and other sensors, cameras for cars’ register plate recognition, and actuators like remotely-controlled door locks or window blind controls), and c) embedded electronics (e.g. industrial machinery, home electronics, smart phones and wearable devices that have embedded parts e.g. processors, data storages, sensors and actuators).

Due to the large diversity of millions of devices, and the consequent distribution of their storage and data analysis resources in order to handle the problem of big data, IoT requires interoperability at multiple levels. On the hardware side, such problems have to be addressed as handling a capability mismatch between traditional Internet hosts and small devices, as well as handling widely differing communication and processing capabilities in different devices. In the interface between the device and network domains, IoT gateways will provide a common interface towards many heterogeneous devices and networks. Some IoT devices, e.g. home electronic appliances will be likely connected directly to the Internet without such middle-boxes. For the communication between heterogeneous IoT devices and applications towards the automated deployment of latter in environments where the former have been already deployed, there is currently a gap of a facilitator technology (interface). Third-party applications that are developed without being aware of devices’ data models (descriptions), but being generic in the sense of being capable of running on various IoT device sets, will not be possible to be automatically deployed. Such inability is caused by the semantic gap between heterogeneous data of both types of entities i.e. devices and applications. Such a gap can be bridged by aligning the meaning of data that both types of entities may ‘carry’ and use these alignments for their semantic matchmaking.

Based on the above ascertainments, distributed and heterogeneous IoT entities need to be consistently, explicitly and formally represented and managed (registered, aligned, composed, and discovered) through suitable abstraction technologies i.e. ontologies. Such a representation and management capability will enable their seamless integration in different application domains of IoT, such as smart home, ambient assisted living, transportation, etc., in a way that deployment of third-party generic applications in non-expert end-users’ IoT settings will be performed automatically, with minimum involvement of both non-experts and experts.

In this paper we focus on the use of semantic technologies, for the automated deployment of heterogeneous and distributed IoT entities, supporting the following three distinct tasks: a) the semantic registration of IoT entities, b) the alignment of IoT entities’ metadata and use of these alignments for their matchmaking, and c) the alignment of the semantics of the data of the messages that are exchanged between these IoT entities during device-to-application communication. We view the deployment of third-party generic applications in such settings as an automated process that hides from end-users the complexity of tasks such as ontology alignment and semantic matchmaking of IoT entities. These complex tasks are not expected to be performed by non-expert end-users but rather they should be supported by an expert third-party service provider e.g. an IoT semantic interoperability as a service (SIaaS) provider that acts as a mediator between IoT application providers and consumers, placing the ontology alignment and semantic matchmaking tasks of the deployment process of IoT entities in a mediation layer of the IoT stack.