clarify on field value

hi,

i would like to clarify below.

1) may i know if the following 3 table fields are storing the same value?

lips-vgbel (reference doc or order) , lips-vgpos (line item)

vbap-vbeln , vbap- line item (forgot the dictionary)

vbfa-vbelv , vbfa-posnv

2) vbap-kwmeng (order quantity) is referring to specific item line order quantity right?

3) vbfa-rfmng is referring to specific item line delivery quantity, right?

4) so to know the open quantity for specific item line, is kwmeng - rfmng. right?

thanks