The EDI Model

There are three logical levels or “layers” of standards required to achieve EDI information transfer, each layer having its own controlling standards organisations (although some organisations may define more than one layer). This structured approach to EDI allows for the maximum flexibility and also enables future developments in technology and standards to be easily incorporated.

From the lowest layer upward, these three layers are:

• The Communications Standards - Defining just how the data is to be transferred from the sender to the receiver.
• The Syntax Standards - Defining what overall standards format the EDI file will be in.
• The Message Standards - Defining exactly what the message is and what information is to be placed where within this message.

These standards are going to be further described in the following sections but it is important to remember that whatever standards are used within each layer, the layering process is required to allow flexibility. For example not all users will wish to use a specific communication protocol; some may even wish to copy the data onto a floppy disk and send it in the post! So the communications level is now a floppy disk but the higher levels still remain.

This principle of multiple methods of achieving the same goal is found over and over again within the EDI regime. It is not an attempt at duplication but is designed to give users the best possible solution and flexibility in all cases.

The Communications Standards are described in a section of their own.

VDA Standard

It should be noted that VDA messages are treated as non-EDI files by most members of the ODEX family. This is because VDA messages are not true EDI messages.

VDA stands for Verband der Automobilindustrie (Motor Industry Association). The VDA is a German automotive standards body which issues the VDA standard documents. VDA messages are not strictly EDI messages as they are simply flat files. Instead of using special characters to divide each segment from the next and each data element from the next, a VDA message consists of fixed length records within which each data element (field) is allowed to take up a specific number of characters. If any item of data is omitted, its absence must be shown by a space the same length as the omitted item of data.

Furthermore, VDA messages do not contain service segments, so there is no concept of interchange or group. However, the first record in a VDA message does contain addressing information of a kind and can therefore be used by an intelligent program such as ODEX Enterprise or DARWIN for routing purposes.

There are enough similarities between VDA messages and true EDI messages to allow VDA messages to be treated by some programs as EDI. VDA messages have a hierarchical structure, meaning that records within a message must adhere to certain rules about the position in which they may appear. VDA records, like EDI segments, also have attributes such as a name, a maximum number of times they may occur and whether their occurrence is mandatory or conditional.

Owing to the differences that exist between the VDA standard and real EDI standards, VDA messages are usually treated as non-EDI files. However, ODEX Enterprise and DARWIN 3 have been programmed to recognise VDA messages and to treat them as if they were real EDI messages.