Question on oslc:occurs

Arthur,

We had a local briefing on last Friday. During the session, we found a new
question about resource shape definition.

> 6.18 oslc:occurs Property
> oslc:occurs is used to specify the number of times that the defined
property may occur. The value of this property MUST be one of the following
individuals:

In my understanding, this oslc:occurs does not specifies the value of
property whether null-able but number of the property. Therefore, in our
shape document, Project:actualStartDate should be oslc:exactly-one but
null-able, since we think it is mandatory but still undecided at the
beginning of the project. Is it correct?

Best regards,
Kaz