`Purchase dependency' refers to the dependency of purchase or non-purchase of one item or itemset on the purchase or non-purchase of another item or itemset. The research in this paper models for incorporating purchase dependencies in retail multi-item inventory management. One illustrative example has been discussed with data mining in retail sale data. Various types of purchase dependencies including negative dependency have been identified and discussed. These purchase dependencies are relevant for inventory management in retail stores. The model with an illustration in this research paper will be motivational to researchers and inventory managers for incorporating purchase dependencies while managing inventory.