Make it much more clear that concrete mapping is limited
Make it much more clear that concrete mapping is limited

Change-Id: Icb2ea787b0defbf5f1244b144759c1e8acff3f0f

monetate/sqlalchemy,sqlalchemy/sqlalchemy,wujuguang/sqlalchemy,monetate/sqlalchemy,graingert/sqlalchemy,j5int/sqlalchemy,wujuguang/sqlalchemy,graingert/sqlalchemy,zzzeek/sqlalchemy,j5int/sqlalchemy