The inventory is not always existing only in a warehouse, and much less common items. Since they are used in a number of processes, some are provided to each process, and some are even stored as a floor inventory. Inventory Holdings refers so-called factory-wide inventory (not only in a warehouse or process). 

As shown in the figure, inventory holdings are mainly divided into Current Inventory and In Process Inventory. Specifically speaking, after items are entered in a warehouse, they are added to the non-allocated inventory of current inventory, and then, according to the item's issue plan, they are transferred to the allocated inventory. After that, when they are actually taken out of the warehouse, they are transferred from the allocated inventory to in process inventory, which are being to controlled in the field.