Abstract
This paper focuses on the application of possibilistic logic in the extension of ontology for uncertain knowledge description. It proposes an uncertain semantic relationship description method based on possibilistic logic and probabilistic statistics. This novel method combines the advantages of subjective valuation and objective statistics, which makes the representation and inference of uncertainty in ontologies more flexible and reasonable. Finally, we apply this quantitative measurement to describe incomplete (uncertain) knowledge and imprecise (vague) information of uncertain knowledge in ontology knowledgebase.