Building smart Internet of Things (IoT) applications requires interchanging and using information from others—whether people or machines—but also needs to understand unambiguously such information. To address this issue, ETSI’s technical committee on Smart Machine-to-Machine Communications (SmartM2M) is leading the Smart Applications REFerence (SAREF) initiative with the goal of bringing a common understanding across cross-domain heterogeneous systems.
The need for a standard ontology for smart applications
IoT fragmentation is one of the main threats in adopting IoT technologies at large scale. In order to overcome this, the current fragmented landscape of IoT technologies requires standardized interfaces and data models to ensure interoperability. In this scenario, one of the main challenges to ensure interoperability is to have a set of standard data models that enable interchanging not only information, but also the meaning of such information to avoid misinterpretations between senders and receivers.
To cope with this, the SAREF ontology was promoted by the European Commission in collaboration with ETSI with the goal of having a common data model to assure interoperability.
Developed in the SmartM2M Technical Committee at ETSI, the SAREF ontology is a data model enriched with formal semantics (Figure 1). It is intended to enable interoperability between solutions from different providers and among various IoT activity sectors, thus contributing to the development of the global digital market.
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Figure 1. An overview of the main classes of SAREF and their relationships. (Source: ETSI)
SAREF explicitly specifies the recurring core concepts in the Smart Applications domain, the main relationships between these concepts, and axioms to constrain the usage of these concepts and relationships. The ontology has evolved over time since its first version published by ETSI in November 2015. Since then, the specification has led to a second version published in March 2017 and a third one published in February 2020.
Furthermore, nowadays IoT solutions require traversing across different vertical domains. Hence, ten different extensions of the SAREF ontology have been produced and published as ETSI standards for different sectors: energy, buildings, environment, smart cities, industry and manufacturing, smart agriculture, automotive, eHealth and ageing well, wearables, and water. This way, SAREF also serves as the glue to interconnect IoT data from different sectors.
SAREF in the IoT ontology landscape
SAREF was not the first and will not be the last ontology in the IoT domain. But, why are there so many? The simple answer is that different ontologies satisfy different needs.
We can take a look at different IoT ontologies already standardized in different bodies, such as the Semantic Sensor Network (SSN) ontology standardized in the World Wide Web Consortium (W3C) or the oneM2M Base Ontology standardized in the oneM2M initiative.
A detailed analysis will show that, while a set of minimal common concepts appears through all of them (i.e., the ability of representing IoT devices and the entities with which they interact), each of the ontologies adds other unique aspects that reflect their intended use. For example, the SSN ontology allows describing system deployments and capabilities, SAREF includes device profiles and tasks and the oneM2M Base Ontology facilitates describing device operations.
One of the main principles followed when developing SAREF is to reuse and align with existing assets. In this sense, the ontology has been developed in order to be compatible with other ontologies, such as the SSN ontology, and has formal alignments with others, such as the oneM2M Base Ontology (Figure 2).
Figure 2. The SAREF ontology addresses multiple sectors and maintains formal alignment with other ontologies such as the oneM2M Base Ontology. (Source: ETSI)
Other key development principles are modularity and extensibility. These are required for SAREF to serve as a coherent and cohesive model that allows interoperability through cross-sectorial data.
This is the unique characteristic of SAREF in the IoT ontology landscape: to gather under a common umbrella not only the way of representing data about devices and their measurements, but also about those particularities required in different domains through its ten current extensions.
The SAREF ontology portal
The SAREF ontology is under continuous development and new extensions are added over time. All the resources related to the SAREF ontology and its extensions are available through the ETSI SAREF website.
On the web, anyone interested in the ontologies can access the latest versions of all the development artefacts, including not only the ontology code but also its documentation, requirements or tests.
Furthermore, since the SAREF ontologies are actively maintained, users can interact with the portal to give direct feedback, pose new requirements, or even propose new extensions for SAREF.
|Raúl García-Castro is Associate Professor at Universidad Politécnica de Madrid. He has been researching for more than fifteen years in ontology development and ontology-based application integration to enable semantic interoperability among systems. In the last decade, he has been actively involved in the development of technical standards in different bodies such as ETSI or the W3C.|