standardised api. In the case of membership for a website, it might
look something like:
get_unique_user_id # of logged in user
get_username_for_id( id )
Then if a forum has tables such as:
thread -> references username
post -> ditto
and maybe methods like
send_pm( user )
find_posts( user )
if you are prepared to sacrifice the actual foreign key relationship,
not that big a thing IMHO, you can do it all through the API. The
person that writes the forum code/schema can actually have two install
options - with and without the user table.
Cat almost has this in place at present.
There's an infinite supply of time, we just don't have it all yet.