Item data refers to the planning factors necessary for the planning and scheduling tools of master scheduling and MRP. Most of it is static and is stored in the computer’s item master file. It includes things like lead times, order quantities, safety stock/time, shrinkage factors, scrap or yield factors (stored in the bill of material).
Getting the item data collected and loaded is a necessary step, but it’s normally not a big problem. The people doing it should be primarily the same ones who’ll be operating these planning systems: the master scheduler(s), material planners, and distribution planners. They’ll need education, time to do the job, and some policy direction.