In a factory, there are a lot of items such as raw materials, parts, and products. But the production planning for all of them is not performed. It is performed for the items handled by sales division such as products and service parts. Customers' demand occurs for such an individual item, and from the standpoint of demand, they have no relationship with each other. On the other hand, the demand of some items depends on that of other items. Such items are e.g. assemblies or parts.

Thus demand Characteristics include independent demand and dependent demand, and the items for which independent demand occurs are called "independent demand item", while the items for which dependent demand occurs are called "dependent demand item"