Approach sounds ok to me.

...but I can just concatenate the various keys together...

That should work, but make sure there is some delimiter between the keys so that you cannot get unintentional overlaps. For instance:

key1  key2  concat concat.
123   45    12345  123.45
12    345   12345  12.345
[download]

Furthermore, you would probably be better off to not expose this key to the outside world, as it contains information about the way your database is structured. You probably want to make an MD5 string out of that so that you have a unique identifier and not expose any information to the outside world.

Liz