Regarding Purchase Invoices Smartform

Hi.I need to develop a purchase invoice smartform.I am having the following fields.

1) g/l Account

2)Narration

3) Posting Date

4)Bill Number

5) Bill DAte

6)PO No

7)PO Text

8)Voucher No

9)Voucher date

10)quantity 11) rate 12)amount13)discount 14 ) sales tax

What are the tables & Fields required for these.I'm not sure whether to take these from rbkp rseg or from purchase tables.

Helpful answers would be appreciated.