An ontology for RAMI4.0 comprising the Administration Shell as a core is provided in this work. The Administration Shell concept provides a semantic description of the elements that describe I40 components. Since the Administration Shell is a key concept of the RAMI4.0 model, we decided to use the namespace rami for the ontology—also, since the ontology implements further concepts of the RAMI4.0 model.
Ontology Overview
In this section, we describe the main classes of the RAMI4.0 ontology (cf. Figure5.2).
rami:AdminShell represents the Administration Shell concept and its properties.
rami:Asset Assets in RAMI4.0 are described by therami:Asset class. In addition, properties
like rami:hasAssetID, foaf:image, anddul:isPartOf, are created to represent characteristics of
the asset.
rami:I40Component this class depicts the concept of the I40 component. An I40 component
characterizes the physical structure of an asset. A given Asset described by an Administration Shell can be considered as an I40 component. I40 components will communicate among each other in I40 environments.
rami:Submodel models the submodel concept in the Administration Shell. The basic data asso-
ciated with the asset are represented byrami:Submodelclass. The classesrami:EnergyEfficiency,
rami:Structure,rami:MESConnection allows to model different types of data, attached to the
Administration Shell concept, as subclasses of therami:Submodel class.
rami:Dimension this class describes the three different dimensions of RAMI4.0, i.e., the
hierarchy level, the IT, and the life-cycle. The three dimensions are represented as subclasses of
therami:Dimension. Moreover, an instance representing every layer in the dimensions is added
to the respective classes. For example, rami:Enterprise is added as an instance of the class
rami:HierarchyLevelDimension to represent the enterprise level of this dimension. Likewise,
the classes rami:View,rami:ExpressionSemanticare populated with instances representing the possible values that they can have. To express this knowledge, the owl:oneOf construct is used. For example, the semantic expressions in RAMI4.0 can only be rami:Confirmation,
rami:Measurement, and rami:Requirement [203]. These concepts are created as instances of the
rami:ExpressionSemantic. Then, they are modeled as the only instances that this class can have
by means of owl:oneOf. This way of modeling is followed in all the classes where the instances can belong to a restricted set of individuals.
Chapter 5 Semantically Describing Industry 4.0 Standards Using Ontologies
Description of Properties
In this section, the core properties of the RAMI4.0 ontology are outlined.
rami:comprises this property connects two of the main classes of the ontology, i.e., the
rami:AdminShelland therami:SubModel.
rami:isConnectedTo links the Administration Shell concept with the different dimensions
described by the RAMI4.0 model.
rami:containsAdminShell describes the connection between the Administration Shell concept
and the I40 component.
rami:describesAsset associates the Asset with the Administration Shell.
rami:inAccordanceWith this property outlines the link between a certain standard and a
given submodel. The standard is described by the sto:Standard class from the STO ontology (cf. Section4.1.1). This approach allows connecting the asset with a given standard that describes it via the Administration Shell [204].
rami:hasDatatype Data types are important for the description of the submodels. This
property points to therdfs:Datatype class to model the connection between a given data type that is used to describe a certain submodel.
rami:hasManifest this property relates the concepts of the Administration Shell and its
correspondent Manifest.
Reusing Well-known Ontologies
Some well-known ontologies are reused to represent the domain of RAMI4.0 and the Adminis- tration Shell concept. The OM ontology is utilized to model the units of measurements. For instance, the class om:Unitas well as the propertyom:hasUnit are used with therami:Submodel
class to represent the units of measurements which are required properties of the submod- els. The SSN ontology is exploited to represent data about sensors. To this end, the classes
ssn:Sensorandssn:Propertyare linked to the submodel rami:SensorMeasurement by using the
ssn:isProducedByproperty. The PROV ontology is reused by means of the classprov:Activity
to describe the activity that generated a specific Administration Shell (rami:AdminShell). In this case, the object property,prov:wasGeneratedBylinks the two classes. The FOAF ontology and the SKOS vocabulary are utilized to represent connections of the classes rami:Assetand
rami:Submodel respectively. The foaf:image property models the image of the asset while
the skos:definition depicts the definition of the Submodel. The identifiers in the RAMI4.0
ontology are added as subproperties of thedcterms:identifierproperty, e.g.,rami:hasAssetId
and rami:hasAdminShellIdare subproperties of dcterms:identifier.
Ontology Design Patterns
We examine the characteristics of the RAMI4.0 model and the Administration Shell to determine which ODP can be reused. Since an asset can be part of other assets and is of interest to obtain the transitivity in this relation, the PartOf ODP is utilized here. Additionally, to encode the relation between the rami:AdminShell and the rami:ComponentManager we employed the Componency ODP. This ODP is expressed through the propertydul:hasComponent to express that therami:ComponentManager is a proper part of a rami:AdminShell.
5.2 The RAMI4.0 Ontology
Figure 5.2: Core classes and properties of the RAMI4.0 ontology. Core concepts related to the RAMI4.0 and the Administration Shell are represented in the diagram. Blue squares depict classes, blue arrows depict object properties and green arrows datatype properties of the RAMI4.0 ontology. Reused classes from well-known ontologies are depicted in white, e.g., SSN, PROV, and OM. Reused properties are shown in black, e.g., DUL, FOAF, SKOS. Green squares show used datatypes.
Units of Measurements
Units are required for specification of products as well as for representing data produced by measuring devices, e.g., sensors. Typically, units of measurements are represented as simple strings, e.g., °C, mm, kg, etc. In such cases, the meaning of units of measurements is not machine-readable and sometimes unknown or ambiguous. For example, both “18 in” and “45,72 cm” are referring to the same length. For properly representing units, an alignment of the
RAMI4.0 ontology with the OM ontology is proposed. By using the in10and cm11concepts from the OM ontology, the semantics of units can be understood by a machine because their formal definitions can be looked up in the ontology via the IRIs of the concepts as well as processed and interpreted by software. For example, “centimetre” is defined as a unit in the dimension of length, amounting to 1/100 of the SI unit “metre”. Listing 5.3illustrates how data values can be represented using the OM ontology and how semantic interoperability conflicts can be addressed.
10
http://www.ontology-of-units-of-measure.org/page/om-2/inch-International
11
Chapter 5 Semantically Describing Industry 4.0 Standards Using Ontologies
@prefix owl: <http://www.w3.org/2002/07/owl#>
@prefix om: <http://www.ontology−of−units−of−measure.org/resource/om−2/>.
@prefix rami:<http://w3id.org/i40/rami/>. rami:asset1 a rami:Asset;
rami:hasLength rami:lengthOfAsset1 .
rami:lengthOfAsset1 om:hasNumericalValue "45.72"^^xsd:float ;
om:hasUnit om:centimetre . rami:asset2 a rami:Asset;
rami:hasLength rami:lengthOfAsset2 .
rami:lengthOfAsset2 om:hasNumericalValue "18"^^xsd:float ;
om:hasUnit om:inch-International . rami:lengthOfAsset1 owl:sameAs rami:lengthOfAsset2.
Listing 5.3: Representing units of measurements with the OM ontology. An example using different units of measurements, i.e., centimeter and inches, to represent the same length of an asset. This representation enables the resolution of the semantic interoperability conflicts of Domain (SIC3) and Representation (SIC4).