UML allows the cardinality of a property to be left unspecified, which is interpreted in UML as a minimum of one and a maximum of one. Properties in an OWL ontology are defined with unspecified cardinalities, but unlike UML, the concept modelling profile interprets the cardinalities of such properties as being zero to many (“0..*”). Thus, if you import an ontology, the cardinalities will be “0..*” by default.
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