A fourth storage policy is full-turnover storage. This policy distributes products over the storage area
according to their turnover. The products with the highest sales rates are located at the easiest accessible
locations, usually near the depot. Slow moving products are located somewhere towards the back of the
warehouse. An early storage policy of this type is the cube-per-order index (COI) rule, see Heskett (1963,
1964). The COI of an item is defined as the ratio of the item's total required space to the number of trips
required to satisfy its demand per period. The algorithm consists of locating the items with the lowest COI
closest to the depot. See also Kallina and Lynn (1976), Malmborg and Bhaskaran (1987, 1989, 1990) and
Malmborg (1995, 1996). A practical implementation of full-turnover policies would be easiest if combined
with dedicated storage. The main disadvantage is that demand rates vary constantly and the product
assortment changes frequently. Each change would require a new ordering of products in the warehouse
resulting in a large amount of reshuffling of stock. A solution might be to carry out the restocking once per
period. The loss of flexibility and consequently the loss of efficiency might be substantial when using fullturnover
storage. The adoption of COI-based storage assignment, or other assignments based on demand
frequency generally require a more ‘information intensive’ approach than random storage, since order and
storage data must be processed in order to rank and assign products (Caron et al. 1998). In some cases this
information may not be available, for example, because the product assortment changes too fast to build
reliable statistics (see De Koster et al., 1999a).