Reference Ontologies

latest update: 2019-11-09  


First a W3C Definition:

An Ontology defines the concepts and relationships used to describe and represent an area of knowledge.

Ontologies are used to classify the terms used in a particular application, characterize possible relationships, and define possible constraints on using those relationships.


The RDL (Reference Data Library) lists the concepts (Classes) in above definition in a taxonomy. That taxonomy has the entity types of the data model of ISO 15926-2 as the top. Below that are their specializations, as applicable to the Process Industries.

In this topic the (to-be-establisched) Reference Ontology, covering the "relationships" in above definition, is outlined. These relationships come in the form of ISO 15926-7/8 Template instances.


For the taxonomy refer to the topic Reference Data. The RDL has a  tree structure of concepts. At the top of this structure is the entity type "Thing", the root node, that applies to all objects. Nodes below this root are more specific concepts.

All ARTEFACTs and some other Class types (e.g. document types) in that taxonomy will be referred to in one or more specialized template instances. These define those "relationships" in above definition that are considered commonly accepted in the Process Industries. A basis for that is the information that the industry wants to store for later use (e.g. resulting from the CFIHOS Project).


The information, as represented with Templates, of a concept lower in a given taxonomic hierarchy, is inherited from a concept higher in that hierarchy.

Below is an example:

Assume the information that all members of the class CENTRIFUGAL PUMP have at ONE TO MANY members of the class PUMP IMPELLER as a part, and that those members of the class PUMP IMPELLER can be a part of ONE TO ONE (so only one at a given dateTime) member of the class CENTRIFUGAL PUMP. Please be aware of the fact that cardinalities in ISO 15926 are just the opposite from the customary cardinalities. See the topic About Cardinalities


    rdf:type tpl:ClassOfAssemblyDefinition ;

    tpl:hasClassOfWhole rdl:RDS416834 ; # CENTRIFUGAL PUMP

    tpl:hasClassOfPart rdl:RDS816299 ; # PUMP IMPELLER

    tpl:hasCardinalityOfWhole rdl:RDS999900701 ; # ONE TO MANY

    tpl:hasCardinalityOfPart rdl:RDS222625 ; # ONE TO ONE

    meta:valEffectiveDate "2019-04-14T21:47:00Z"^^xsd:dateTime .


  • For the ID of the template instance we use the RDS number of the main Object Of Interest plus a suffix, so that it can be addressed (see below);
  • The text behind # does not belong to the code, but is for your information only ;
  • Normally the RDS number is referred to, but in the browser the rdfs:label of the class is shown instead for easier readability ;
  • Using the valEffectiveDate it is possible to generate the version of the ontology at a particular dateTime to the granularity of individual classes and templates.

One of the many specializations of CENTRIFUGAL PUMP is the class RADIAL FLOW PUMP that happens to have one or more RADIAL FLOW PUMP IMPELLERs as part.

The related template instances is coded as follows:


    rdfs:subClassOf :RDS416834-0001 ; # above template instance

    tpl:hasClassOfWhole rdl:RDS12957061 ; # RADIAL FLOW PUMP

    tpl:hasClassOfPart rdl:RDS461384 ; # RADIAL FLOW PUMP IMPELLER
    meta:valEffectiveDate "2019-04-17T09:23:00Z"^^xsd:dateTime .



Here we only show what is different from higher up in the taxonomic hierarchy. It is advisable, though, to show everything here, because relying on inheritance would become unmanageable (possible overloading of RDL endpoint, reliance on uptime of that server).

Life-cycle Information

Assume that the XYZ Corp. has the following information about a requirements class for their radial flow pump P101 with the tag CO-P101 (CO = ClassOf):


    rdf:type tpl:ClassOfAssemblyDefinition ;

    rdfs:subClassOf rdl:RDS12957061-0001 ;

    tpl:hasClassOfWhole xyz:3d6c9348-14b1-4773-bb74-d1cd30ba6f24 ; # elsewhere declared CO_P-101, a local specialization of <RADIAL FLOW PUMP> (see Note)

    tpl:hasClassOfPart xyz:d7286636-a0e3-4e5e-99be-d84d7ec02ffd ; # elsewhere declared CO_P-101-IMP, a local specialization of <RADIAL FLOW PUMP IMPELLER>

    tpl:hasCardinalityOfWhole rdl:RDS999900701 ; # <TWO TO TWO> overriding the <ONE TO MANY> in :RDS416834-0001 (see first Note below)

    tpl:hasCardinalityOfPart rdl:RDS222625 ; # <ONE TO ONE>, inherited from :RDS416834-0001

    meta:hasLifecycleActivity rdl:RDS2226731 ; # ROTATING EQUIPMENT ENGINEERING

    meta:valEffectiveDate "2019-04-18T11:16:33Z"^^xsd:dateTime .



  • Assume that xyz:3d6c9348-14b1-4773-bb74-d1cd30ba6f24 is, at a later date as the engineering progressed, also specialized from TWO STAGE CENTRIFUGAL PUMP. That means that the hasCardinalityOfWhole becomes TWO TO TWO. It also means that the template shown above has replaced the initial template which had the inherited hasCardinalityOfWhole of ONE TO MANY ;
  • The rdfs:subClassOf relation for the specialization of Templates is new in this context ;
  • If so required the template instance could be validated because of its link to the Reference Ontology ;

SME Input

Needless to say that this set-up can only bear fruits when the SMEs (Subject Matter Experts) of the various fields of expertise will give their input. If not, the ontologies will be limited to assembly models. The results of the CFIHOS Project will be such a source, as well as the LOPs (List Of Properties) of IEC for instrument ontologies.