This paper introduces the SAREF reference ontology pattern SAREF4SYST, which defines systems, connections between systems, and connection points to which systems can be connected. These basic concepts can be used generically to define the topology of entities of interest and can be specialised for multiple domains. SAREF4SYST has already been reused or aligned to in diferent domains related to cyberphysical systems, including electrical power systems, smart buildings and smart lifts, communication networks, and multiphysics simulations.
semantic interoperability.
In this paper we introduce the first such SAREF reference ontology pattern SAREF4SYST,
which defines systems, connections between systems, and connection points to which systems
can be connected. SAREF4SYST has been published as ETSI Technical Specification (TS) 103 548
in 2019 as part of previous STF 556 "Consolidation of SAREF and its community of users, based
on the experience of the EUREKA ITEA - 12004 SEAS" [
The rest of this paper is organised as follows. Section 2 provides general application scenarios for the pattern. Then Section 3 overviews the ontological description of the pattern and how it may be used in diferent domains. Finally Section 4 discusses some of its influences and uptake.
SAREF4SYST defines Systems, Connections between systems, and Connection Points at which systems may be connected. These core concepts can be used generically to define the topology of features of interest, which is knowledge relevant for use cases in various application domains of Cyber-Physical Systems.
SAREF4SYST can be used for example to describe zones inside a building (systems), that share frontiers of diferent types (connections). Properties of systems are typically state variables (e.g. temperature, volume, energy, mass), while those of connection points are typically interaction capacities and flows (e.g. thermal transmittance, energy flow, matter flow, impedance).
The following paragraphs illustrate the applicability of SAREF4SYST in three diferent domains. Note that modeling properties of features of interest is not part of SAREF4SYST. Power Energy. In the Smart Energy domain, electric power systems can exchange electricity with other electric power systems. The electric energy can flow both ways in some cases (from the Public Grid to a Prosumer), or in only one way (from the Public Grid to a Load). Electric power systems can be made up of diferent sub-systems. Generic sub-types of electric power systems include producers, consumers, storage systems, transmission systems.
Electric power systems may be connected one to another at electrical connection points. An Electric power system may have multiple connection points (Multiple Winding Transformer generally have one single primary winding with two or more secondary windings). Generic sub-types of electrical connection points include plugs, sockets, direct-current, single-phase, three-phase, connection points.
An Electrical connection may exist between two Electric power systems through two of their respective connection points. Generic sub-types of electrical connections include Single-phase Buses, Three-phase Buses. A single-phase electric power system can be connected using diferent configurations at a three-phase bus (phase 1-to-neutral, phase 2-to-neutral, phase 3-to-neutral). Smart Building. Buildings, Storeys, Spaces, are diferent sub-types of Zones. Zones can contain sub-zones. Zones can be adjacent or intersect with other zones. Two zones may share one or more connections. For example some fresh air may be created inside a storey if it has two controllable openings to the exterior at diferent cardinal points. Lifts have one or more openings, and evolve in a shaft. Storeys may have openings to the shaft. Both the lift openings and the storey openings may have doors that may be in an open or closed state. Communication networks. Smart devices contain microcontrollers with Input/Output ports and RadioFrequency (RF) communication modules of diferent kinds. Wired communication may be established between two devices directly, and between two or more devices through some bus. RF communication from a sender to receivers may be established at a certain radiofrequency, with each party powering its RF module at a certain level, and receivers having a relative measure of the Received Signal Strengh Indicator (RSSI) and Signal-to-Noise Ratio (SNR).
SAREF4SYST consists both of a core ontology, and guidelines to create ontologies applying the SAREF4SYST ontology pattern. The core ontology is a lightweight OWL-DL ontology that defines 3 classes and 9 object properties. It uses namespace https://saref.etsi.org/saref4syst/ prefixed as s4syst: and is available as open source at https://saref.etsi.org/sources/saref4syst/ under the ETSI BSD-3 license, and is submitted as Architectural ODP on the ontologydesignpatterns.org website as http://ontologydesignpatterns.org/wiki/Submissions:SAREF4SYST.
Figure 1 provides a general overview of these classes and properties. In this figure, rectangles are used to denote classes. Plain arrows are used to represent Object Properties between classes. The origin of the arrow is the domain of the property, and the target of the arrow is the range of the property. Dashed arrows with identifiers between stereotype signs (i.e. "« »") refer to OWL axioms that are applied to some property. Four pairs of properties are inverse one of the other; the property s4syst:connectedTo is symmetric, and properties s4syst:hasSubSystem and s4syst:subSystemOf are transitive. A symbol =1 near the target of an arrow denotes a cardinality of 1. A symbol ∃ denotes a local existential restriction.
hasSubSystem <<transitive>>
subSystemOf <<transitive>> <<inverseOf>> connectedTo <<symmetric>> =1 connectionPointOf connectsAt
Connection System <<inverseOf>>
ConnectionPoint connectedThrough
∃ connectsSystem <<inverseOf>>
∃ connectsSystemThrough connectsSystemAt <<inverseOf>>
A s4syst:System is defined as a part of the universe that is virtually isolated from the environment. The system properties are typically state variables (e.g. consumed or stored energy, agent population, temperature, volume, humidity). Figure 2 illustrates classes and properties that can be used to define connected systems and their sub-systems.
This module reuses the PartOf ODP. A connection between two s4syst:Systems, modelled
by s4syst:connectedTo, describes the potential interactions between connected s4syst:Systems.
For example s4lift:canConnectToNetwork, from the SAREF extension for Smart Lifts
(SAREF4LIFT [
s4syst:connectedTo is symmetric. Sub-properties, however, are not necessarily symmetric, and can be defined for example to model that some matter only flows from one system to the other. For example property s4lift:connectedToEmergencyBattery links a s4lift:ElectricPowerSystem system to another that is its emergency battery.
These core entities are defined as follows:
A connection can be qualified using class s4syst:Connection. Figure 3 illustrates classes and properties that can be used to qualify connections between s4syst:Systems.
These core entities are defined as follows: s4syst:Connection. The class of connections between systems. This class qualifies property s4syst:connectedTo. A connection describes potential interactions between systems. Any two connected systems are connected through a connection. A connection can connect more than two systems at the same time. s4syst:connectsSystem. Links a connection to one of the systems it connects. s4syst:connectedThrough. Links a system to one of its connections to other systems.
A s4syst:System connects to other s4syst:Systems at connection points. A connection point belongs to one and only one s4syst:System, and can be described using the class s4syst:ConnectionPoint.
Figure 4 illustrates the classes and the properties that can be used to describe connection points of a s4syst:System. One can then associate a s4syst:ConnectionPoint with properties (saref:Property) that describe it (e.g. position and speed, voltage and intensity, thermal transmittance).
These core entities are defined as follows: s4syst:ConnectionPoint. The class of connection points of systems, at which they may be connected to other systems. This class qualifies properties s4syst:connectsSystem and s4syst:connectedThrough. A connection point belongs to exactly one system. Any system connected through a connection is connected at one of its connection points to the connection. The system of a connection point that is connected through a connection is itself connected through the connection. s4syst:connectionPointOf. Links a connection point to the one and only one system it belongs to. s4syst:connectsAt. Links a system to one of the connection points at which it connects. s4syst:connectsSystemThrough. Links a connection point to one of the connections through which it connects its system. s4syst:connectsAt. Links a connection to one of the connection points at which it connects a system.
Furthermore, the following sub-property chain axioms are defined:
s4syst:connectsSystem ⊑ s4syst:connectsSystemAt s4syst:connectionPointOf s4syst:connectedThrough ⊑ s4syst:connectsAt s4syst:connectsSystemThrough (1) (2)
These allow to infer that a connection at a connection point necessarily connects the system of that connection point (Axiom 1), and that if a connection point connects its system through a connection, then the system is connected through this connection (Axiom 2).
ETSI TS 103 548 [
The label of the sub-property should use the same morpho-syntactic structure as its super-property. ([14, Clause 5.3.3.2])
The technical specification also guides the users in choosing the type of axioms that may be appropriate for the pattern application.
A sub-property of the s4syst:connectedThrough property may have an inverse property. If defined, the English-tagged labels and comments of these two properties shall reflect this aspect. ([14, Clause 5.3.3.2]) A sub-class of the s4syst:System class may have an existential restriction on a sub-property of s4syst:connectedThrough to some sub-class of s4syst:Connection ([14, Clause 5.3.3.2])
SAREF4SYST is the result of incorporating the seas:SystemOntology ontology into SAREF,
which is one of the core modules of the Smart Energy Aware Systems (SEAS) ontology [
The SAREF extension for Smart Lifts (SAREF4LIFT [
Examples Smart Lift Installation1 and Smart Lift General Configuration 2 illustrate the use of the SAREF4SYST pattern and its diferent classes and properties.
s4lift:connectedToEmergencyBattery
s4lift:hasStandardPowerSupply
Several works have closely or remotely adopted the patterns behind SAREF4SYST.
The TUBES System Ontology (TSO) and the Flow System Ontology (FSO) align to
SAREF4SYST for the description of flow systems in buildings. TSO aims to explicitly define
the hierarchical, structural, and functional aspects of interconnected building service systems
in the Architecture Engineering, and Construction (AEC) industry and their relationships to
spatial entities throughout their whole life cycle. FSO aims to describe the matter and energy
lfow between systems and components, and the composition of such systems [
SAREF4SYST is used by Bjørnskov and Jradi [
Roxin et. al. in [
SAREF4SYST is the first SAREF Reference Ontology pattern. It has proven to be useful to model various types of system, connection through which these systems interact in some way, and the connection point at which these systems connect. More patterns for SAREF are currently being discussed in the context of STF 578 "SAREF Patterns", and should be described beside SAREF4SYST in a new version of ETSI TS 103 548.
This work has been partly supported the ETSI Specialist Task Forces 556 "Consolidation of SAREF and its community of users, based on the experience of the EUREKA ITEA - 12004 SEAS", and CoSWoT projet (grant ANR-19-CE23-0012 from Agence Nationale de la Recherche, France).