Uncertainty in KR

How should missing, incomplete, or uncertain knowledge be represented in an ontology?

Some relevant conferences:

UAI : Uncertainty in AI
URSW : Uncertainty Reasoning for the Semantic Web

Literature

See also uncertainty in category theory and statistical relational learning. The latter is about ML for relational databases and thus, indirectly, knowledge representation.

Books

Halpern, 2017: Reasoning about Uncertainty, 2nd ed.