Incremental Transaction Number on Multiuser Environment

Hi..

I have a problem about How to generate Incremental Transaction Number on Multiuser environment ?

for example : 13070001, 13070002, 13070003, etc..

This number is generated when users open a new transaction so when a User Interface displayed, that number is already on database and user can't look that number on their screen.

What I'm afraid here is about more than one user open new transaction and then when my business object generate that number ,then writed on DB Primary Key Collision Happened ?

is there any suggestions ? or any idea is ok,

thanks a lot

stefanus