When generating OntoUML stereotypes, every fact type that does not match a more specific rule is labelled as a material relation.

A material relation states that a separate relationship object exists that makes the relation hold. For a fact type where nothing in the model points to such a relationship, that is an assertion the model does not support, and it is the kind of blanket labelling that makes the stereotypes less informative: if everything is material, the label carries no information.

Expected: fact types between two object types may still default to material, but the remaining cases are left without a stereotype rather than being labelled by default. The generator already omits the label when no stereotype applies.

Optionally this can be reported as a model quality finding, so unclassified fact types are visible instead of silently labelled.