WMS Elements in PM Order

Hi All,

I)

Will you pls explain the difference between three WBS Elements shown in maintenance order.

those are as follows:

1) WBS in location tab of PM Order (in a/c assignment screen area)

2) WBS in additional data tab (in orgnization screen area)

3) WBS in settlement rule

II)

Actually I want a BApi which can fetch all above fields but which bapi I have got it contains only two WBS...so I am not getting 3rd one.....Please help...

Sundar