Maintaining PBDNR values in PBIM Table

Hi,

I would like to know how to maintain "PBDNR" values in PBIM Table and what is the main use of "PBDNR" as we already have"BDZEI" which is "Independent requirements pointer".

Please guide me 1)how to maintain values for "PBDNR" and also "BDZEI" along with transasction code and

2)what possible values can the "PBDNR" and "BDZEI" can have.

Thanks in advance for ur support.