A group of data elements which together describe an item which is part of or contained within a multiple-component or multiple-item product or a trade pack. The composite must be used with all multi-component or multi-item products and packs to specify (for example) the item(s) and item quantities included in a combined book plus audiobook product, a multi-volume set, a filled dumpbin, or a classroom pack. In other cases, where parts are not individually identified, it is used to state the product form(s) and the quantity or quantities of each form contained within the product. The composite must be repeated for each individually-identified item or component, or for each unidentified type of item or component.

Each instance of the <ProductPart> composite must carry a <ProductForm> code and a quantity, even if the quantity is ‘1’. If the composite refers to a number of copies of a single item, the quantity must be sent as <NumberOfCopies>, normally accompanied by a <ProductIdentifier>. If the composite refers to a number of different items of the same form, without identifying them individually, the quantity must be sent as <NumberOfItemsOfThisForm>.