This document presents the implementation of the SAREF extension for the water domain (SAREF4WATR) which based on a limited set of use cases and from available existing data models. This work has been developed in the context of the STF 566 which was established with the goal to create SAREF extensions for the domains of automotive, eHealth and ageing well, wearables, and water.

### General overview

Figure 1 and Figure 2 present an overview of the classes and the properties included in the SAREF4WATR extension.

Figure 1: SAREF4WATR overview. Measurements and KPIs
Figure 2: SAREF4WATR overview. Water-related terms

### Measurement

As it can be observed in Figure 3, the modelling of measurements in the SAREF4WATR ontology mostly relies on the measurement model proposed in SAREF.

SAREF allows to define the temporal extent of a measurement by defining the timestamp for it (using the saref:hasTimestamp property). However, the SAREF4WATR extension also required to be able to define the temporal interval to which a measurement applies, apart from the temporal instant defined by the timestamp. Therefore, the s4watr:hasPhenomenonTime property has been defined in this extension to define the time for which the measurement applies to a feature of interest. The range of this property time has been defined as a time:TemporalEntity, which allows defining temporal intervals or instants.

Besides, the extension requires to be able to represent those devices that measure a certain feature of interest (and those features of interest that are measured by a device) independently of having measures from which this relationship could be inferred. Because of this, in this extension we have created four new properties to relate saref:Device and saref:FeatureOfInterest: s4watr:featureIsMeasuredByDevice, s4watr:featureIsControlledByDevice, s4watr:measuresFeature, and s4watr:controlsFeature.

Figure 3: Measurement model

### Water meter

Figure 4 provides an overview of how to represent a water meter using the s4watr:WaterMeter class. The representation of water meters and their properties has been extracted from the European M-Bus standard (EN 13757).

A water meter may be defined by the properties inherited from SAREF (e.g., saref:hasManufacturer or saref:hasModel) and also by a set of properties defined in SAREF4WATR to indicate: its fabrication number (s4watr:hasFabricationNumber), its firmware version (s4watr:hasFirmwareVersion), its hardware version (s4watr:hasHardwareVersion), its version (s4watr:hasVersion), the radio frequency in which it operates (s4watr:operatesAtRadioFrequency), and its required power (s4watr:requiresPower).

Measurements may be taken from the water meter themselves. To enable the representation of such measurements, water meters are defined as features of interest (saref:FeatureOfInterest) and a non-exhaustive list of properties has been defined based on the M-Bus standard to allow measuring: on time (s4watr:MeterOnTime), operating time (s4watr:MeterOperatingTime), battery operating time (s4watr:BatteryOperatingTime), battery last change (s4watr:BatteryLastChange), and battery remaining time (s4watr:BatteryRemainingTime).

Figure 4: Water meter model

### Water flow

Water meters are mainly intended to measure water flows. SAREF4WATR defines the main properties related to the water flow that are defined in the European M-Bus standard (EN 13757): pressure (s4watr:FlowPressure), rate (s4watr:FlowRate), temperature(s4watr:FlowTemperature), and volume(s4watr:FlowVolume). These properties are depicted in Figure 5.

Figure 5: Water flow model

There are also other environmental factors that are relevant since they affect water and the infrastructures using it. Therefore, the following environmental properties, depicted in Figure 6, are defined: atmospheric pressure (s4watr:AtmosphericPressure), humidity (s4watr:Humidity), precipitation (s4watr:Precipitation) and temperature (s4watr:ExternalTemperature).

Figure 6: Environmental properties model

### Tariff

SAREF4WATR allows describing the tariff that is applied to a water meter by means of the s4watr:Tariff class, as presented in Figure 7. The representation of tariffs has been extracted from the CEN/TR 17167 technical report.

A tariff may be described using different properties to describe its: start timestamp (s4watr:hasStartTimestamp), duration (s4watr:hasDuration), period (s4watr:hasPeriod), billing date (s4watr:hasBillingDate), and billing period (s4watr:hasBillingPeriod). Besides, a tariff can be related to a water meter by means of the s4watr:appliesTo property. There are different types of tariffs, depending on whether they are based on thresholds (s4watr:ThresholdBasedTariff), consumption (s4watr:ConsumptionBasedTariff), or time (s4watr:TimeBasedTariff). Each of these types of tariffs has its own properties: for threshold-based ones their volume flow can be defined (s4watr:forVolumeFlow), for consumption-based ones their volume and financial consumption can be defined (s4watr:forVolumeConsumption and s4watr:forFinancialConsumption, respectively), and for time-based ones their absolute time at day, week day and day in month can be defined (s4watr:forAbsoluteTimeAtDay, s4watr:forWeekDay and s4watr:forDayInMonth, respectively). It is also possible to define a combined tariff by making it an instance of more than one type of tariff.

Figure 7: Tariff model

### Water types

SAREF4WATR defines four types of water as instances of the s4watr:Water class: raw water (s4watr:RawWater), drinking water (s4watr:DrinkingWater), storm water (s4watr:StormWater), and waste water (s4watr:WasteWater). All these types of water, depicted in Figure 8, are defined as features of interest (saref:FeatureOfInterest), so measurements and key performance indicators can be defined over them.

Figure 8: Water types model

### Water properties

SAREF4WATR includes a classification of the different water properties based on the classification proposed by the World Health Organization, as shown in Figure 9. Water properties (s4watr:WaterProperty) are classified into acceptability (s4watr:AcceptabilityProperty), chemical (s4watr:ChemicalProperty), and microbial (s4watr:MicrobialProperty) ones, being bacterial (s4watr:BacterialProperty) properties a subclass of microbial ones. The extension defines different individuals for each type of water property, based in different EC directives on the quality of drinking water, bathing water, and groundwater. This list of individuals does not aim to be exhaustive but to reflect the potential use of the ontology. Note, for example, that it is out of the scope to categorize chemical compounds according to their intended use (e.g., pesticide, fertilizer, etc.).

Figure 9: Water properties model

### Water infrastructure

In SAREF4WATR water infrastructures can be defined using the s4watr:WaterInfrastructure class. Such infrastructures may be designed for one of the water types described above (through the s4watr:isDesignedFor property), may have an intended use (through the s4watr:isIntendedFor property), and may be classified into five different types, although others may be defined if needed: distribution systems (s4watr:DistributionSystem), storage infrastructures (s4watr:StorageInfrastructure), treatment plants (s4watr:TreatmentPlant), hydroelectric power plants (s4watr:HydroelectricPowerPlant), and monitoring infrastructures (s4watr:MonitoringInfrastructure).

In order to represent the topology of a water infrastructure or its assets, the GeoSPARQL ontology has been reused and connected to the SARE4WATR terms. As shown in Figure 10, for representing spatial objects the geosp:SpatialObject class from GeoSPARQL has been reused along with its subclasses that allow defining spatial features (geosp:Feature) and geometries (geosp:Geometry). Different properties from GeoSPARQL can be reused to define spatial relations among spatial objects (e.g., geosp:sfContains, or geosp:sfWithin)or to define the geometry of a feature (geosp:hasGeometry). Two types of geometries from the GeoSPARQL Simple Features ontology are proposed to be used: points (sf:Point) and polygons (sf:Polygon), although others may also be used from that same ontology or from another one. We refer to the GeoSPARQL standard for further details on how to define the topology of water infrastructures.

Figure 10: Water infrastructure model

By reusing the SAREF4SYST ontology, the different subsystems of a water infrastructure may be defined. A water infrastructure is a complex system (s4syst:System) and each of its subsystems may be defined (using the s4syst:hasSubSystem property) as a water asset (s4watr:WaterAsset).

As shown in Figure 11, SAREF4WATR defines the main types of water assets found in the literature in a hierarchy that is not intended to be exhaustive and that may be extended if needed. This hierarchy classifies water assets into source assets (s4watr:SourceAsset), sink assets (s4watr:SinkAsset), storage assets (s4watr:StorageAsset), and transport assets (s4watr:TransportAsset).

A dedicated class has been defined for water devices (s4watr:WaterDevice), which are those water assets that are also devices according to SAREF (saref:Device). A water meter, described above, is one special type of water device, among other possible water-related sensors and actuators.

Figure 11: Water asset model

### Key Performance Indicator

Figure 12 provides an overview of the modelling of Key Performance Indicators (KPI). The KPI modelling involves two main concepts, namely s4city:KeyPerformanceIndicator and s4city:KeyPerformanceIndicatorAssessment. As can be seen in the figure, the modelling of KPIs in SAREF4WATR totally relies on the KPI model proposed in SAREF4CITY.

In SAREF4WATR, KPIs are intended to be defined for water infrastructures (s4watr:WaterInfrastructure). However, KPIs may also be defined for other features of interest.

Figure 12: Key Performance Indicator model