Prduct formed out of a group of products

I am modifying the zen cart so that I can add some products which are group of other products
Existing product A, B, C, D

New product can be defined as

Product E = 1xA + 2XB + 5XC + 3XD

So, when a customer is purchasing product E, the inventory of A gets reduced by 1, B by 2, C by 5 and D by 3
Also, if there are only 20 units of C available, then only 4 units of E should be shown in stock

Is it possible to do so using attributes or changing the code would be the best way to do it?

I was thinking of adding one more column to the products table known as special_products = yes or no
and then one more table with master product id and child product id and quantity

Any suggestions?