EDIFACT Basics: Segments, Elements and the Envelope in 10 Minutes
Every VDA message - 4984, 4987, 4938 and the rest - is an EDIFACT file at heart. Ten minutes of syntax makes every implementation guide dramatically easier to read.
The three-level envelope
UNB ... interchange header (sender, receiver, control ref)
UNH ... message header (type, version)
BGM, DTM, NAD, LIN ... the actual business content
UNT ... message trailer (segment count, control ref)
UNZ ... interchange trailer (message count, control ref)
An interchange (UNB…UNZ) is the envelope; inside it sit one or more messages (UNH…UNT); inside each message sit segments. VDA files usually contain exactly one message per interchange.
Segments, composites, elements
A segment starts with a three-letter tag and ends with '. Inside, + separates data elements and : separates the parts of a composite element:
DTM+137:20260925:102' | | | +- format code (102 = CCYYMMDD) | | +- the date value | +- qualifier "137" = document date +- segment tag
An empty element keeps its separator: NAD+ST++123456::92' has an empty second element.
The service string advice (UNA)
If a file starts with UNA, its six characters redefine the separators (component, element, decimal mark, release character, reserved, segment terminator). Most VDA files use the defaults (UNA:+.? ') and many omit UNA entirely.
The release character
? escapes a separator that appears inside real data: IMD+++BRACKET?+SET::92' contains a literal +. Parsers that forget this rule misalign everything after the first escaped character.
Code lists, not free text
Most qualified elements use numeric codes from UN/EDIFACT code lists: 137 for document date, 351 for DESADV, 92 for "assigned by buyer". The VDA guidelines then restrict these lists to the codes each OEM accepts - which is why a code that is perfectly legal EDIFACT can still be rejected by a customer.
Reading tip
When a guideline says "DTM+137 required, format 102", you now know exactly which four characters to look for. Our validators surface the same view: tag, qualifier, value, format - one segment per line.