what's the right table structures for one-to-many forms?

eg. for invoicing, I use:

invoice.dbf
---------------
inv_no
inv_date
cust_id

inv_detail.dbf
------------------
inv_no -> foreign key of invoice.inv_no
stock_id
qty
price

while my friend insists the right way is:

invoice.dbf
---------------
inv_pk
inv_no
inv_date
cust_id

inv_detail.dbf
------------------
inv_fk -> foreign key of invoice.inv_pk
stock_id
qty
price

in his opinion, the key shoud be meaningless, not represent anything.

while my way (using invoice number) will cause lots of problem in the future, espesially with SQL databases.

please advise.

regards,

Jerry