the demand of a customer is expressed by a value that represents the total weight of the items to be delivered, while in real-world instances demands consist of sets of items which are characterized not only by a weight but also by a shape.
A more detailed modeling of such characteristics can involve additional issues such as, e.g., handling loading and unloading operations, dealing with fragile items, operating with automatic forks, and so on.
A first complication of the basic models arises when we want to ensure that the transported items can be feasibly allocated within the vehicle loading space. A second possible complication may come from the fact that the unloading operations should be performed without reshuffling the transported items, hence they are affected by the order in
which the items are loaded and/or by the items position within the loading area.
Problems
related to the former complication are briefly reviewed below, while details on the latter
are discussed in the specific sections.