A clarification on odrl:duty

Hi,

According to ODRL 2.1 ontology [1], the odrl:duty property [2]
has Permission class as the domain and Action/Duty classes as the range.
The examples in the document illustrate the same. However, the diagram [3],
it shows that duty is a relationship between a Policy [e.g., Offer] and a
Rule [e.g., Duty].

Is there an inconsistency in the diagram or am I reading it wrong?

Best Regards,
Nandana

[1] https://www.w3.org/ns/odrl/2/ODRL21
[2] https://www.w3.org/ns/odrl/2/ODRL21#term-duty
[3] https://www.w3.org/ns/odrl/2/diagram.png