What is the applicability of defining item category key flex fields?

Summary:We have a requirement that , our client have a segmented category structure. so to integrate the same ,we need to define item segment categories in oracle fusion. We have already created the category segments under item category structure. However, after deployment I could not see any fields under "Manage functional area catalog.

Content (required):We have a requirement that , our client have a segmented category structure. so to integrate the same we need to define item segment categories in oracle fusion. We have already created the category segments under item category structure. However, after deployment I could not see any fields under "Manage functional area catalog.