There are no constraints on the cardinality of the skos:notation property. A concept may have zero, 1 or more notations.
Where a concept has more than 1 notation, these may be from the same or different notation systems. In the case where notations are from different systems, different datatypes may be used to indicate this. It is not common practice to assign more than one notation from the same notation system (i.e., with the same datatype URI).
gezever
commented
2 years ago
https://www.w3.org/TR/skos-reference/#notations 6.5.2. Multiple Notations
There are no constraints on the cardinality of the skos:notation property. A concept may have zero, 1 or more notations.
Where a concept has more than 1 notation, these may be from the same or different notation systems. In the case where notations are from different systems, different datatypes may be used to indicate this. It is not common practice to assign more than one notation from the same notation system (i.e., with the same datatype URI).