COMMONS — Need to be able to indicate whether or not something can only be classified by a single classifier from a specific scheme

This is not expressible in OWL, easily. One option would be to create a boolean that indicates this is the case, which perhaps a rule engine for data quality, or sparql, or a SHACL shape could then test. What you really want to be able to say is that 'is classified by' can only have one value from a given classification scheme when applied to something.

This is a change to the Classfiers ontology, which may impact that section of the specification.

Supporting this feature should be done in a user ontology, but we provide a flag for those that might need it

The simplest way to say that only one member of a specific classification scheme can be used to classify something is to add a restriction to the concept in question. Something like

ClassifiedItem isClassifiedBy max 1 SpecificClassifier

where the classified item is the concept in a user ontology being classified, and specific classifier is the one from the scheme that applies. For example, suppose that the classification scheme / controlled vocabulary includes the individual paint colors that are available to customize a vehicle for purchase for some model/model year and manufacturer. A vehicle manufactured by that manufacturer that is of that model and model year can only have one color from that scheme, i.e.,

Vehicle isClassifiedBy exactly 1 VehicleColor

where the VehicleColor is a member of that specific scheme.

We could complicate the classifiers ontology to add several new classes, such as ClassifiedThing, UniquelyClassifiedThing, SpecificClassificationScheme (or ExclusiveClassificationScheme) and SpecificClassifer, where the SpecificClassifier is a member of the ExclusiveClassificationScheme, where all members of the scheme are disjoint/different from one another, and where a UniquelyClassifiedThing can be classified by max 1 SpecificClassifier. The FTF agreed that this would overly complicate the ontology, though, and that commons users can add the restriction on the thing that they are classifying as needed without requiring the "clutter".

We will provide a boolean flag, called isExclusive to allow users that need it to add such a flag to their classification scheme.