This part of ISO/IEC15459 specifies a unique, non-significant, string of characters for the unique identifier for grouping of transport units. The character string might be represented in a bar code label or other AIDC media associated with the items that make up the grouping to meet supply chain needs and regulatory needs (e.g. customs clearance). An individual instance of an entity is aptly identified by a unique identifier defined in other parts of ISO/IEC15459. This relationship has to be communicated to the business partners according to the business need and the unique identifier for the grouping might be used as a reference number only or marked in addition to the existing identifier. To address management needs, different classes of items are recognized in the various parts of ISO/IEC15459, which allows different requirements to be met by the unique identifiers associated with each class. This part of ISO/IEC15459 defines the rules for the grouping of transport units to identify the multiple physical units that make up a single shipment from a consignor and are treated as a single logical grouping for customs and other shipping requirements.