Any database object, except for a property itself, can have a property added/attached to it. (For a property of a property, you would need to create a hierarchical property object). You should be able to do what you want using the dbCreateProp() function:
=> d_prop / nil
For certain properties, e.g. time, which looks like a string, you need to use a specific function, dbCreateTimeProp() for example.
I hope that this helps you.