Category

[Questions King]

My question is how to create the relationships for Category? In my Inventory have many Product ID but diffent Category. So I use define values list(use values from field) relationships to Inventory Product ID. So every time I select the field will show all Product ID, now I try to use Category to control the Product ID. Look like when I select the select Category only show the category Product ID at the field.

Any idea to do it??? Pls. Advice.....