No, that kind of "extension table" is a well-known antipattern being fragile, unscalable, and denormalized. Just a table with columns for id, keyname & metadata about the key will do.
Not exactly, I wouldn't be afraid of the data table having both attribute name & value columns. EAV is practically 6NF which would prohibit that. (to be honest that id field was out of habit, the known-keys table should probably be unique and indexed on the key name)
I'm sorry, but I'm still unsure what you mean. A "known-keys table" is not a common term in the literature. Can you give an example by describing the tables and their columns?
Ok, I agree. This is the reason why I was asking :-)
> Just a table with columns for id, keyname & metadata about the key will do.
Isn't this the Entity-Attribute-Value model (which has the well known drawback of requiring a join for each attribute)?