What is the purpose of the database port on the ZR5 installation screen?

It seems to come up before you pick whether you're using ZCM or config file, which I find odd.

The docs seem to indicate that if you select ZCM config, it'll know about whatever database ZCM is using (ie: external MS SQL or Oracle, etc.)
But by then you've already set a database port?

So what should we use for the Database port? Is that the port that our Oracle database is (for ZCM?)
Or does ZR5 use some other database as well as whatever ZCM is using?

If the latter, WHERE does this database get installed and what is it used for?

(this is obviously different than ZRS)