I would assume that the rdbms tag is easily assumed for just about every question on dba.stackexchange.com.
For those questions specifically about non-relational DBMSen, the non-relational tag can be used.
Is the rdbms tag redundant? Should it be removed in edits and deprecated?
databasegets my vote too :) – Jack Douglas♦ May 13 '11 at 17:35databasetag has been removed from nine questions. Hope we are all agree with keepingrdbmstag. – Coder Hawk May 16 '11 at 12:50