Yugang Yu and colleagues have published results of a recent study entitled, "Optimal zone boundaries for two-class-based compact three-dimensional automated storage and retrieval systems" in Iie Transactions. The study explains that compact, multi-deep three-dimensional (3D), Automated Storage and Retrieval Systems (AS/RS) are becoming more common, due to new technologies, lower investment costs, time efficiency and compact size, and that decision-making research on these systems is still in its infancy. The paper studies a particular compact system with rotating conveyors for the depth movement and a Storage/Retrieval (S/R) machine for the horizontal and vertical movement of unit loads.