1. Introduction
Internet of Thing (IoT) is machine-to-machine communications and interactions between objects, devices and people. In the near future the communications and information processing will be ubiqutious and performed by IoT systems.
Over the past few years the semantics community has developed ontologies to describe concepts and relationship between different entities in various domains. The Internet of Things (IoT) domain have similar approaches to apply semantics. A key problem is that most of the IoT related semantic descriptions are not as widely adopted as expected. One of the main concerns users and developers have is that semantics increase the complexity and processing time and therefore they are unsuitable for dynamic and responsive environments such as the IoT.
Complex models, although can be applied for querying almost anything about objects, are often difficult to implement and use. They need high processing and therefore they are not suitable for constrained environments. IoT models should consider the constrains and dynamicity of the IoT environments. At the same time, they need to model the relationships and concepts that represent and allow interoperability between IoT entities. Therefore, expressiveness versus complexity is a challenge.
We propose IoT-Lite, a lightweight instantiation of the semantic sensor network (SSN) ontology 1 to describe the key IoT concepts that allows interoperability and discovery of sensory data in heterogeneous IoT platforms. IoT-lite reduces the complexity of other IoT models describing only the main concepts of the IoT domain. IoT-Lite can be extended by different models to increment it expressiveness.
IoT-Lite describes IoT concepts in three classes. Objects, system or resources and services. IoT devices are classified into, although not restricted to, three classes: sensing devices actuating devices and tag devices.
IoT-Lite is focused on sensing, although it has a high level concept on actuation that allows any future extension on this area.
Services are described with a coverage. This coverage represents the 2D-spatial covered by the IoT device.
The figure below depicts the concepts of the ontology and the main relationships between them.
IoT Lite Ontology is created to be used with a common quantity taxonomy,
qu-taxo,
to describe the Units
and QuantityKind
that IoT devices can measure. This taxonomy is represented by individuals in the ontology and is based on well-known taxonomies such as:
qu
and qudt.
Similarly, some other classes, such as Object, Service or Attribute, can be linked to a vocabulary to choose the terms from a set of individual and existing concepts.
2. Example
The following is an example of an annotated temperature sensor belonging to one of the TelosB devices of the Surrey testbed, SmartCampus.
The example in Turtle (REF) is:
Example
@prefix qu: <http://purl.org/NET/ssnx/qu/qu#> .
@prefix geo: <http://www.w3.org/2003/01/geo/wgs84_pos#> .
@prefix ssn: <http://www.w3.org/2005/Incubator/ssn/ssnx/ssn#> .
@prefix iot-lite: <http://purl.oclc.org/NET/UNIS/fiware/iot-lite#> .
@prefix iot-l-ins: <http://purl.oclc.org/NET/UNIS/iot-lite/iot-liteInstance#> .
iot-lite:tableRoom13CII01 rdf:type iot-lite:Object ,
owl:NamedIndividual ;
iot-lite:interfaceDescription "http://surrey.ac.uk/sensor/Room13CII01/Table"^^xsd:anyURI ;
iot-lite:hasAttribute iot-lite:tempreratureTableRoom12CII01 ;
geo:hasLocation iot-l-Ins:locationRoom13CII01 .
iot-lite:temperatureTableRoom12CII01 rdf:type iot-lite:Attribute ,
owl:NamedIndividual ;
iot-lite:isAssociatedWith iot-l-Ins:temperatureSensorRoom13CII01 ;
iot-lite:hasQuantityKind qu:temperature .
iot-l-Ins:NEcornerRoom13CII01 rdf:type owl:NamedIndividual ,
geo:Point ;
geo:long "-0.59316"^^xsd:float ;
iot-lite:altRelative "1stFloor"^^xsd:string ;
geo:lat "51.2434"^^xsd:float .
iot-l-Ins:SWcornerRoom13CII01 rdf:type owl:NamedIndividual ,
geo:Point ;
geo:long "-0.59315"^^xsd:float ;
iot-lite:altRelative "1stFloor"^^xsd:string ;
geo:lat "51.2433"^^xsd:float .
iot-l-Ins:TelosB001 rdf:type owl:NamedIndividual ,
ssn:Device ;
ssn:hasSubsystem iot-l-Ins:temperatureSensorRoom13CII01 .
iot-l-Ins:UniSTestbed rdf:type owl:NamedIndividual ,
ssn:System ;
ssn:hasSubsystem iot-l-Ins:TelosB001 .
iot-l-Ins:areaRoom13CII01 rdf:type iot-lite:Rectangle ,
owl:NamedIndividual ;
iot-lite:hasPoint iot-l-Ins:NEcornerRoom13CII01 ,
iot-l-Ins:SWcornerRoom13CII01 .
iot-l-Ins:locationRoom13CII01 rdf:type owl:NamedIndividual ,
geo:Point ;
geo:long "-0.593154"^^xsd:float ;
iot-lite:altRelative "1stFloor"^^xsd:string ;
geo:lat "51.243362"^^xsd:float .
iot-l-Ins:ngsi10SensorRoom13CII01 rdf:type iot-lite:Service ,
owl:NamedIndividual ;
iot-lite:endpoint "http://surrey.ac.uk/sensors/measures/rom13CII01"^^xsd:anyURI ;
iot-lite:interfaceDescription "http://surrey.ac.uk/sensors/measures/room13CII01"^^xsd:anyURI ;
iot-lite:type "ngsi-10"^^xsd:string .
iot-l-Ins:resolution1024 rdf:type iot-lite:Metadata ,
owl:NamedIndividual ;
iot-lite:metadataValue "1024.0"^^xsd:float ;
iot-lite:type "resolution"^^xsd:string .
iot-l-Ins:sensorRoom13CII01 rdf:type owl:NamedIndividual ,
ssn:Deployment ;
geo:hasLocation iot-l-Ins:locationRoom13CII01 .
iot-l-Ins:temperatureSensorRoom13CII01 rdf:type owl:NamedIndividual ,
ssn:SensingDevice ;
iot-lite:hasCoverage iot-l-Ins:areaRoom13CII01 ;
iot-lite:exposedBy iot-l-Ins:ngsi10SensorRoom13CII01 ;
ssn:hasDeployment iot-l-Ins:sensorRoom13CII01 .
iot-l-Ins:temperatureSensorTelosB rdf:type owl:NamedIndividual ,
ssn:Sensor ;
iot-lite:hasMetadata iot-l-Ins:resolution1024 ;
iot-lite:hasSensingDevice iot-l-Ins:temperatureSensorRoom13CII01 ;
iot-lite:hasUnit qu:degree_Celsius ;
iot-lite:hasQuantityKind <http://purl.org/NET/ssnx/qu/quantity#temperature>.
3. IoT Lite Ontology at Glance
An alphabetical index of IoT Lite terms, by class (concepts) and properties are given below. All the terms are hyperlinked to their detailed description for quick reference.
Classes: ActuatingDevice, Attribute, Circle, Coverage, Metadata, Object, Polygon, Rectangle, Service, TagDevice,
Properties: relativeLocation, altRelative, interfaceDescription, endpoint, exposedBy, hasAttribute, hasCoverage, hasMetadata, hasPoint, hasQuantityKind, hasSensingDevice, hasUnit, id, isAssociatedWith, radius, type, value,
4. Cross-reference for IoT Lite classes and Object Properties
