I don't have a good answer for this. So bear with me. Maybe the salesperson example is bad, because of the context. I.e. a valid node id is numeric, where is a usable one is somewhere below this node number at creation time, something higher in the future.

I probably shouldn't have specific data checking that is DB related built in.

Btw, in the US, zipcodes are all 5 digit,then and extra 4. 00000-0000 is valid in syntax,but not in the context of being available, or usable. Just as the name xxxxxxyyyyy isvalid in most countries that use the alphabet, but you can't pronounce it.

Thoughts?