Message Standards

In our telephone analogy, our telephone callers may exchange information because both parties are speaking the same language and understand the protocols that they must use, but unfortunately the remote party still does not understand the information that the caller is giving because they are from different industries and each industry has its own jargon and sequence or layout of information. To get over this problem the final layer of the EDI model was developed, in which both trade-specific and general document standards are defined by the controlling organisations.

It should be mentioned at the outset that the message standards are subject to different interpretations and even misuse by some trading partners, so it is vital to get agreements between partners not only about the message standards used but also about the exact meaning and contents of information, before EDI interchanges are exchanged. Many large organisations publish their own implementation manuals for the standards that they wish to use. Even though these standards are based upon an industry standard message, there may well be minor differences in layout and format.

The EDIFACT message standard is the most widely used in Europe. EDIFACT is a general-use standard not linked to any particular industry and is controlled by the EDIFACT board closely associated with both the EAN numbering associations and the United Nations. For the automotive industry there is ODETTE (Organisation for Data Exchange by Tele-Transmission in Europe) and VDA (Verband der Automobilindustrie). ODETTE have historically had their own standards but have, since 2000, adopted the EDIFACT standards. The VDA standard is not a true EDI standard but does have many similarities. Many other industry specific organisations exist, such as CEFIC for the chemical industry and TRADACOM for the retail industry.

So what is a message standard? From the introductory section you will have learned about the need to code a paper document’s information into electronic form. In the previous sections we have looked at ways of moving data electronically and ways of getting a computer to understand the format (syntax) of a file by splitting it up into messages, segments and data elements. Now all that is left is to define exactly what item of information is going to be contained in which segment, element, etc. That is the purpose of the message standards.

Each message standard is firstly defined by a structure diagram detailing the segments and where they occur. Each segment on the structure diagram is defined as having a number of attributes. These are a name, a maximum number of occurrences and a mandatory or conditional status. The segment is drawn on the diagram as shown below.

Here we see a NAD segment (NAD segments are used by EDIFACT to define Names and Addresses) where the segment name is held in the top section of the diagram. The segment is Mandatory ( M ) meaning that it must occur at least once in the message. The alternative to mandatory is Conditional ( C ) meaning that it need not occur if there is no information to be held in it. The segment is repeating ( R ) which means that it may occur more than once. An invoice, for example, may have more than one item line on it. Alternatives to this are the number 1 for a segment that may only occur once, or a number defining the maximum number of times that the segment may occur.

Message Structure

Many of these segment diagrams are combined together to form a message structure diagram. The message structure is hierarchic, meaning that segments may appear at a number of different levels and some segments will act as “parents” and “children” to others to define more complex pieces of information. To take a simple example, an item of goods appearing on a document, an invoice or order perhaps, would have a basic description held in a parent segment and then be further defined by child segments under the parent which describe its dimensions, its cost, its markings and many other attributes. These child segments may themselves be parents to more detailed segments, for example the segment holding the price may have date information segments under it as the price changes with time.