Business Objects(BOs) & Data Transfer Objects(DTOs)-both needed ?

In a J2EE system...

I know that "Business Objects" (BOs) are basically value objects (VOs) ...lots of getters and setters and some business logic. These are basically to model nouns in the system. Eg Student BO.

I know that "Data Transfer Objects" (DTOs) are value objects (VOs)....with getters and setters... with the purpose of avoiding multiple method calls...to avoid overhead...which effects performance. eg it's better to pass a Student DTO then say...pass the student ID and student name and student age etc etc.

Main question : Should a system have both ? If yes, why do I need a StudentBO.java and then another StudentDTO.java....when they are so similar ?...when both are basically VOs ? Can't I just use BOs to serve as DTOs ?

Thanks.

[778 byte] By [bw_ta] at [2007-10-2 5:32:10]