Some products must recorded in inventory database differently. For example: Shoes are stored by models and after stored by sizes.
I think There is no regular solution about that.
I have an idea. Size inventory saved under main product.
For example : Shoe model is DK64836 ( Brown leather shoe with white lines ).
Size 42 - Stock QTY : 11
Size 43 - Stock QTY : 5
Size 44 - Stock QTY : 7
Size 45 - Stock QTY : 22
Total stock is : 55
This stock management feature needed on most of textile products.