Write some Software online stock management for online store

manage online stock by implementing the following rule: we are selling our products as singles & groups, groups products consisting from different components of single items, we need to system update the online stock of group products when any update on the quantities of singles are changes, like the following role: we have single items like A , B and C, and group products like: AB or BC or AC or ABC, when any of the single items quantity of any single item is changed, sold or added, the quantity of the related grouped products should be updated accordingly. for more details & clarifications, please let me know.