[inopinatus]

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)

[ngrilly]

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?