This topic is to show how our proverbial pump P-101 fits in ISO 15926.
The blue part shows a subset (~10%) of the ISO 15926-2 data model, starting with ClassOfIndividual and PossibleIndividual. These are specialized as shown.
The RDL - Reference Data Library in the green part contains instances of the subclasses of ClassOfIndividual (and many other things that are not relevant in this context). These are also subclasses of subclasses of PossibleIndividual (see ARTEFACT in above diagram).
Most instances of (subtypes of) ClassOfInanimatePhysicalObject start, in the top of their hierarchy, with being a specialization of an instance of ClassOfFunctionalObject. In above diagram CENTRIFUGAL PUMP SYSTEM is a subclass of the instance PUMP SYSTEM of ClassOfFunctionalObject. (NOTE - a PUMP SYSTEM has a BARE PUMP as a part).
CENTRIFUGAL PUMP SYSTEM, or any of its many subclasses (not shown) is the superclass of a so-called Requirements Class in the brown part, often defined in a Specification (here, in this example for pump P-101, such as an API 610 Pump Data Sheet).
That Requirements Class classifies pump P-101 in the ochre part, or actually a temporal part thereof. How this is done has been worked out in the topic "Plant Life-cycle Model". P-101 is an instance (member) of PUMP SYSTEM (its essential function), InanimatePhysicalObject, WholeLifeIndividual, and NonActualIndividual (because it exists in the Design World, see the PossibleWorlds topic).
Already on the P&ID it is shown with the symbol of CENTRIFUGAL PUMP. So we classify a temporal part as such. Later, when the specification has been declared, we classify another temporal part with that Requirements Class.