how to make a private attributes in STI?

rubyonrails-talk
1

people table like this

id int not null auto_increment, type varchar not null /* common attributes */

name varchar not null, email varchar not null, /* attributes for type=Customer */

balance decimal(10,2), /* attributes for type=Employee */

2

my silly question is though the autoer note which attribute belong who, but in the real world, real code, how can I know which is private attribute for customer or employee?

any thought here?