confused about the relationship between koji and pungi

[Chen Baozi]

hello,
i'm a novice for system building and have read some articles about pungi and
koji recently. but i'm a little confused about the relationship between the
tools. in my opinion, pungi is focusing on building iso while koji is
focusing on building packages. and i'm wondering if the koji has got some
similar functions as pungi does, or is it simply that we use koji to
build packages and then make tree/iso by pungi?