Vendor-Managed Inventory (VMI) is a theory based inspired by integration in supply chain management. In recent years, various partnerships like vendor managed inventory (VMI) approach have been used in inventory management as a method to cope with the bullwhip effect such. In the traditional inventory management, a retailer (sometimes called buyer) makes his own decisions regarding the order size while in VMI, a retailer shares his inventory data with a vendor (sometimes called supplier) such that the vendor is the decision-maker who determines the order size for both. Thus, the vendor is responsible for the retailer's ordering cost, while the retailer has to pay for his own holding cost. This policy can prevent stocking undesired inventories and hence can lead to an overall cost reduction. Moreover, the bullwhip effect is also reduced by employing the VMI approach in a buyer–supplier cooperation.
As replenishment frequencies play an important role in integrated inventory models to reduce the total cost of supply chains which many studies fail to model it in mathematical problems. VMI is a family of business models in which the buyer of a product provides certain information to a supplier (vendor) of that product and the supplier takes full responsibility for maintaining an agreed inventory of the material, usually at the buyer's consumption location (usually a store). A third-party logistics provider can also be involved to make sure that the buyer has the required level of inventory by adjusting the demand and supply gaps.
As a symbiotic relationship, VMI makes it less likely that a business will unintentionally become out of stock of a good and reduces inventory in the supply chain. Furthermore, vendor (supplier) representatives in a store benefit the vendor by ensuring the product is properly displayed and store staff are familiar with the features of the product line, all these while helping to clean and organize their product lines for the store. VMI can also decrease the magnitude of the bullwhip effect.
One of the keys to making VMI work is shared risk. In some cases, if the inventory does not sell, the vendor (supplier) will repurchase the product from the buyer (retailer). In other cases, the product may be in the possession of the retailer but is not owned by the retailer until the sale takes place, meaning that the retailer simply houses (and assists with the sale of) the product in exchange for a predetermined commission or profit (sometimes referred to as consignment stock). A special form of this commission business is scan-based trading, where VMI is usually applied but its use is not mandatory. This is one of the successful business models used by Walmart and many other big box retailers. Oil companies often use technology to manage the gasoline inventories at the service stations that they supply (see Petrolsoft Corporation). Home Depot uses the technique with larger suppliers of manufactured goods. VMI helps foster a closer understanding between the supplier and manufacturer by using electronic data interchange formats, EDI software and statistical methodologies to forecast and maintain correct inventory in the supply chain. Vendors benefit from more control of displays and more customer contact for their employees; retailers benefit from reduced risk, better store staff knowledge (which builds brand loyalty for both the vendor and the retailer), and reduced display maintenance outlays.
Consumers benefit from knowledgeable store staff who are in frequent and familiar contact with manufacturer (vendor) representatives when parts or service are required. Store staff have good knowledge of most product lines offered by the entire range of vendors. They can help the consumer choose from competing products for items most suited to them and offer service support being offered by the store. At the goods' manufacturing level, VMI helps prevent overflowing warehouses or shortages, as well as costly labor, purchasing and accounting. With VMI, businesses maintain a proper inventory, and optimized inventory leads to easy access and fast processing with reduced labor costs.
Classes in Vendor-Managed Inventory
1- Bi-Level VMI Mathematical Models
The first class of VMI, bi-level VMI mathematical model, includes two levels (or echelons) in a supply chain: vendor and retailer. There are three types of VMI mathematical models developed from this class, which are single-vendor single-retailer VMI model, single-vendor multi-retailer VMI model, and multi-vendor multi-retailer VMI model. This class has been significantly developing. For example, single-vendor single-retailer VMI model was extended for multi-product case, the consignment stock (CS), and discount.
2- Multi-Level VMI Mathematical Models
The second class is multi-level VMI mathematical model such as a single manufacturer-single vendor multi-retailer (SM-SV-MR) VMI model. Those studies fail to model replenishment frequencies cannot classified here. As replenishment frequencies play an important role in integrated inventory models to reduce the total cost of supply chains which many studies fail to model it in mathematical problems.