Q:

Logical data model - how to indicate optional FK?

If a logical data model is modelling entities with optional foreign keys, how is that indicated on the model? I'm looking at one now, where, for example, we have:
COUNTRY 1:1 ----------- 0:N TRANSACTION

The TRANSACTION entity contains a country attribute that may or may not have a value. I would have thought that in this case, the optionality of the FK would be shown as:
COUNTRY 0:1 ----------- 0:N TRANSACTION

Is that correct? Or does the 1:1 also imply "IFF a value is provided"?

A:

The short answer is that you're correct. If a TRANSACTION has an optional association with a COUNTRY, then using min-max notation we would indicate
COUNTRY 0:1 ----------- 0:N TRANSACTION

1:1 doesn't imply "IFF a value is provided", it explicitly states a value must be provided.

