Division 1.2 UN/EDIFACT message structure

The message structure is based on ISO 9735.

UN/EDIFACT messages are composed of segments. The structure of a message is described in a branching diagram indicating the position and the mutual relationship of the segments and segment groups.

For each segment data elements are defined: some data elements are combined to form composite data elements. A segment and a data element within a segment are either mandatory (M) or conditional (C). Mandatory segments and/or data elements contain important data for a receiving application and shall be filled with valid data.

Each message starts with two or three segments, the ‘interchange header’ (UNB) and the ‘message header’ (UNH). Where required, also the ‘service string advice’ (UNA) is used as a first segment to define which character sets are used in the message. Each message finishes with the segments ‘message trailer’ (UNT) and ‘interchange trailer’ (UNZ). Thus, each message is contained in one interchange, and an interchange contains only one single message.