The Smart Applications REFerence Ontology (SAREF)

A Brief History of SAREF

The SAREF initiative started in 2014/2015 with a study requested by the European Commission on "Available Semantics Assets for the Interoperability of Smart Appliances: Mapping into a Common Ontology as a M2M Application Layer Semantics" [i.1]. Such study acknowledged that the energy utilization of Smart Appliances can be reduced if they are managed and controlled on a system level. The system needs standardized interfaces to ensure interoperability. Many of the required standards already exist, but a common architecture does not, resulting in a market which is too fragmented and powerless. Therefore, a reference ontology of consensus was designed to cover the needs of all appliances relevant for energy efficiency. The study consisted of three tasks:

• Task 1: Take stock of existing semantic assets and use case assets.
• Task 2: Perform a translation exercise of each model (or use case) to a common ontology language and a mapping or matching exercise between all the models.
• Task 3: Propose a reference ontology and document the ontology into the ETSI M2M architecture.

NOTE: The ETSI M2M architecture has evolved into the oneM2M architecture, therefore the latter one was considered.

About 50 different semantic assets (i.e. standards, protocols, data models, ontologies) had been identified that describe various properties of Smart Appliances in residential environments. After translating half of these semantic assets into Web Ontology Language (OWL) (https://sites.google.com/site/smartappliancesproject/ontologies), 20 recurring concepts were used as initial building blocks for creating the Smart Applications REFerence ontology. The concepts were mapped from the semantic assets to SAREF to allow for translations between different semantic assets [i.3].

In November 2015, SAREF was transformed into a Technical Specification and published by ETSI SmartM2M as ETSI TS 103 264 [i.4].

In 2016, ETSI SmartM2M requested a Specialist Task Force (STF) to identify and create possible extensions of SAREF, and provide input to update SAREF according to the requirements collected from the stakeholders that have used SAREF since its first release in April 2015. This led to a new release SAREF V2.1.1 [i.5], which incorporated the feedback both from the STF that created the first SAREF extensions, and from the stakeholders that provided their input for improving SAREF. This feedback can be found in ETSI TR 103 411 [i.2] and was used to create SAREF V2.1.1.

The scope of the first release of SAREF was limited to an indoor managed domain, such as a building managed by a building manager or an apartment managed by a user. This scope also included the outdoor premises that belong to the considered indoor managed domain, in other words, a pergola that is part of the building is also within the scope, as well as a sensor located under that pergola. Note that the smart city domain was not originally considered, i.e. if the same sensor that is under the pergola is also in a street, then the sensor in the street was out of the scope of SAREF. After extending SAREF to different domains, it was clear the need for broadening the scope of SAREF from home appliances and buildings to any device that can be found in smart applications; this motivated the change of name of the ontology from "Smart Appliances REFerence ontology" to "Smart Applications REFerence ontology".

In June 2018, another STF started in SmartM2M with the goal (among others) of consolidating SAREF with new reference ontology patterns, based on the experience from the EUREKA ITEA SEAS project. As a result of this STF, 37 different issues were identified and discussed in ETSI TR 103 549 [i.8], proposing and agreeing on resolutions for most of them. Furthermore, it was identified the need for moving some transversal terms used in several extensions of SAREF to the core SAREF ontology, because of the broad applicability of such terms. This led to the release of SAREF Core V3.1.1 [i.6].

SAREF and its different extensions were developed quite independently by different teams of experts, sometimes in parallel. Sometimes different modelling decisions were made, with the result that SAREF extensions had important discrepancies. SmartM2M started to identify ontology patterns that may be used to homogenise the structure of SAREF extensions. In 2022, two new STFs started in SmartM2M with the goal to homogenise and facilitate the use of SAREF and existing 11 SAREF domain mapping by using common ontology patterns. A total of 91 different issues were identified and discussed in ETSI TR 103 781 [i.9], and a set of SAREF Core reference ontology patterns was specified in ETSI TS 103 548 [i.10]. These STFs also published a SAREF Core V3.2.1 [i.7] in January 2024, using updated reference ontology patterns [i.10] to solve the harmonization needs [i.9] with updated development framework and tools [i.11].

A summary of the most relevant changes made in the different versions of SAREF Core is available in annex A of [i.7].