UN/EDIFACT Standard: Basis for EDI communication
The UN/EDIFACT standard has developed in response to the growing need for a common standard for data transmission using EDI facilities that is platform independent. UN/EDIFACT is defined as the United Nations rules for Electronic Data Interchange for Administration, Commerce and Transport. They comprise a set of internationally agreed standards, directories and guidelines for the electronic interchange of structured data, and in particular that related to trade in goods and services, between independent computerised information systems. A UN/EDIFACT transmission consists of one or more UN/EDIFACT messages, each of which consists of logically grouped segments. An interchange begins with a UNB segment and ends with a UNZ segment. Each message starts with a header segment (UNH) and ends with a trailer segment (UNT). An optionally included UNA segment preceding the UNB segment is used to ‘set’ the syntax characters to be used.
Depending on size and type, messages can be divided into three distinct sections: header, detail and summary. A header section will contain data that is relevant to the whole message. The detail section contains data relevant to a particular item that can occur a number of times within a message (e.g. invoice line, customs item). The summary section contains summary and control information relevant to the whole message. Sections are often separated by UNS segment (e.g. CUSDEC) but may not always be the case (e.g. CUSCAR message).
A data segment is an intermediate unit of information in a message. It consists of a set of pre-defined, functionally related data elements and has a three letter identifier. Segments can be mandatory or conditional. In general, only specified segments (such as the service segments (start with UN), header segments and certain trailer segments) are mandatory. Each data segment is terminated by a special character inserted in the data segment immediately following the last data element to be transmitted. The quote ( ‘ )character is typically used as the segment terminator. It should be noted that the mandatory or conditional status of a segment, composite or data element is not directly related to the mandatory or conditional status of any data items required for a specific Customs procedure in the message used. For example “country of origin code” may be mandatory data for a Customs procedure in a particular country but may not be required in the application of the same procedure in another country. If the segment is designated as mandatory in the UNSM it will always have to be transmitted. This will cause problems for the country that does not require the data. If the segment in the UNSM is designated as conditional, the country not requiring the data will not have to transmit the segment. However the country which requires the data can indicate in their user manual for the message that the data must always be transmitted. As messages are designed for as wide a use as possible segments with a status of mandatory are kept to a minimum.