Rickerism

Nested Representation

X12 and EDIFACT both contain the implied (or interpreted) structure of loops within the messages. A loop is a set of associated segments. Generally, if the first segment of a loop appears in a message, then the other segments of the loop should also appear.

The most common example of a loop is a mailing address. In X12, an address loop will usually contain the following segments:

• N1 Name
• N2 Additional Name Information
• N3 Address Information
• N4 Geographic Location
• NX2 Location ID Component
• REF Reference Identification
• PER Administrative Communications Contact

It is very convenient to be able to handle segments within a loop collectively. Grouping segments of a loop aids in understanding, processing and displaying WS-EDI messages. As such, WS-EDI Level 2 representation introduces a loop structure.

Loop

Not all segments belong to a loop. Loops can contain segments and other loops. We identify a loop by the first segment contained in the loop. With these points in mind, consider the following schema change for WS-EDI Level 2:

	<!ELEMENT wsedi ((segment|loop)+)>
	<!ELEMENT loop (segment,(segment|loop)*)>
	<!ATTLIST loop
	    code CDATA #REQUIRED>

An address loop, or N1 loop, in X12 would look something like the fragment provided here:

	<wsedi>
	...
	<loop code="N1">
	  <segment code="N1">...
	  <segment code=”N2″>…
	  <segment code=”N3″>…
	  <segment code=”N4″>…
	</loop>

Interchanges and functional groups

EDI documents can contain several messages. The EDI document or file itself is called an interchange. An interchange will contain one or more functional groups. A functional group will contain one or more messages. In a simple EDI document, we would have one interchange containing one functional group containing one message. Sometimes EDI is not so simple.

The following document fragment shows how WS-EDI Level 2 would represent the document nesting of an EDIFACT message.

<wsedi>
  <segment code="UNA" name="Service String Advice"/>
  <segment code="UNB" name="Interchange Header"/>
  <loop code="UNG">
      <segment code="UNG" name="Functional Group Header"/>
      <loop code="UNH">
          <segment code="UNH" name="Message Header"/>
          ... segments and loops of message ...
          <segment code="UNT" name="Message Trailer"/>
      </loop>
      <segment code="UNE" name="Functional Group Trailer"/>
  </loop>
  <segment code="UNZ" name="Interchange Trailer"/>
</wsedi>

The WS-EDI document could contain more than one UNG loop and each UNG loop could contain several UNH loops.

The following fragment shows the document nesting structure for X12.

<wsedi>
  <segment code="ISA" name="Interchange Header"/>
  <loop code="GS">
      <segment code="GS" name="Functional Group Header"/>
      <loop code="ST">
          <segment code="ST" name="Message Header"/>
          ... segments and loops of message ...
          <segment code="SE" name="Message Trailer"/>
      </loop>
      <segment code="GE" name="Functional Group Trailer"/>
  </loop>
  <segment code="IEA" name="Interchange Trailer"/>
</wsedi>

Example documents

• An UN EDIFACT document and its Level 2 representation.
• An ANSI X12 document and its Level 2 representation.