Electronic Data Interchange
The Interchange Header (ASC/X12)

The Interchange Header is the starting control segment of the interchange envelope.  After the recipient has received the document, the interchange header is the first data segment encountered in the document.  The interchange header contains:

• the sender and receiver information,
• authorization and security information,
• date and time interchange was created,
• standard version of interchange structures,
• the control number that uniquely identifies the interchange, and
• identifies the element separator, repetition separator, component separator and data segment terminator.

This topic covers:

• Interchange Header in a Document
• Identifying Delimiters
• Programmatically Reading the Interchange Header
• Programmatically Generating the Interchange Header

Interchange Header in a Document

In the document, the interchange header is identified with the first letters "ISA" followed by the element separator.

The interchange header data stream fits into the implementation guideline defined for the interchange header as follows:

REF	ELE	NAME	REQ	TYPE	MIN/MAX	VALUE	COMMENT
01	I01	Authorization Information Qualifier	M	ID	2/2	00	This element qualifies the value entered in element position 02 (DE I02).  The "00" code indicates that there is no authorization information stored there.
02	I02	Authorization Information	M	AN	10/10	0000000000	This value is not meaningful as stated by data element in position 01 (DE I01).
03	I03	Security Information Qualifier	M	ID	2/2	01	This data element qualifies the element in position 04 (DE I04).  The "01" code indicates that the value stored there is a password.
04	I04	Security Information	M	AN	10/10	MYPASSWORD	Password value as indicated by the element in position 03 (DE I03).
05	I05	Interchange ID Qualifier	M	ID	2/2	ZZ	This element qualifies the value entered in element position 06 (DE I06).  The "ZZ" code indicates that the value stored there is mutually defined.
06	I06	Interchange Sender ID	M	AN	15/15	SENDERISA	This value identifies who was the sender of the interchange.  Since this value is mutually defined as specified by element position 05 (DE I05), this sender identity is meaningful only to the trading partner.
07	I05	Interchange ID Qualifier	M	ID	2/2	ZZ	This element qualifies the value entered in element position 08 (DE I07).  The "ZZ" code indicates that the value stored there is mutually defined.
08	I07	Interchange Receiver ID	M	AN	15/15	RECEIVERISA	This value identifies who is the intended recipient of the interchange.  Since this value is mutually defined as specified by element position 07 (DE I05), this recipient identity is meaningful only to the trading partner.
09	I08	Interchange Date	M	DT	6/6	090419	The date in "YYMMDD" format.
10	I09	Interchange Time	M	TM	4/4	1548	The time in "HHMM" format.
11	I65	Repetition Separator	M		1/1	!	Repetition separator.
12	I11	Interchange Control Version Number	M	ID	5/5	00503	Interchange version 00503.  "Standards Approved for Publication by ASC X12 Procedures Review Board through October 2005"
13	I12	Interchange Control Number	M	N0	9/9	000000020	Number assigned to the interchange so as to be unique from other interchanges in the document.  The interchange trailer pair should have the same number.
14	I13	Acknowledgment Requested	M	ID	1/1	1	The value "1" indicates that the sender is requesting an interchange acknowledgment at receipt of the interchange.  The value "0" is used otherwise.
15	I14	Interchange Usage Indicator	M	ID	1/1	T	The value "T" indicates that this interchange is for testing only.  For production, use "P"; for Information, use "I".
16	I15	Component Element Separator	M		1/1	>	Component element separator.

Identifying Delimiters

The delimiters of each interchange in the document is determined from the interchange header alone.  The following is the process how each delimiters are discovered:

• Element Separator .  The element separator is identified as the character immediately following the interchange header identifier, ISA.
  
  

  

• Segment Terminator.  Each element in the interchange header is of fixed length as indicated by its minimum the same as its maximum length.  Because each element is also defined to be mandatory (its presence is required), the entire length of the interchange header is also fixed.  So based on the definition of the interchange header above, the data length plus the element separators that follow each value totals to 104 characters.  The string between the end of the 104th character and the start of the functional group header is determined to be the segment terminator.  The start of the functional group header is the string that makes up the functional group identifier and the element separator that follows it: GS*.  The segment terminator is determined this way based on the fixed 104th character, as opposed to counting data elements, because the length of the segment terminator is not known.
  
  

  

• Component Separator.  The component separator is the character specified by the data element I15 of the interchange header.
  
  

  

• Repetition Separator.  The repetition separator is the character specified by the data element I65 of the interchange header.
  
  

  

Properly specifying the delimiters in the interchange header is critical to processing the document correctly.  The interchange header is the first data stream encountered in the document, and by its raw information one can determine the nature of the data enveloped by the interchange entity.  The delimiters dissect the raw data in the interchange header into its known constituents.  These information are:

• Data element separator .  This is the most important information acquired from the raw data.  It must:
  • Immediately follow the interchange header.  The first character extracted is determined to be the element separator, whatever that character may be, either text or binary (see above).
  • Be distinct from all separators or terminators.  It must especially be different from the repetition separator and component separator because these two separators are contained in the interchange header itself.  The element separator is required to separate the separator characters from other characters in the interchange header.  If the repetition or component separator is identical to the element separator, the wrong data can be extracted from the interchange header, and  Framework EDI may not be able to detect this severe error condition which can result from inconsistent and erroneous behavior.
• Interchange Control Version Number.  The version information is used to select the implementation guideline to verify the syntactical correctness of the interchange header.  The version is read from the raw data at the twelfth data element of the interchange header after the segment identifier.  Extracting this data requires counting element separators and extracting whatever data lies between the twelfth and thirteenth element separator.  The correctness of this data depends on the how correct the element separator is.  Counting element terminators as opposed to using the fixed length information to determine the version information is done to overcome the possibility that the interchange header in the actual document may not be the expected length due to corruption, inadvertent modification, etc.
  

  
  The repetition separator determined above is "!" (exclamation mark), and the version is "00503".  The diagram below demonstrates what happens if the repetition separator is identical to the element separator, that is, the "!" is replaced by "*".

  
  Based on the erroneous raw data, the repetition separator is translated as empty, and the control version number is translated as empty as well.

Programmatically Reading the Interchange Header

The following steps demonstrates how to read the interchange header.

• Create an instance of ediDocument.

  Dim oEdiDoc As Fredi.ediDocument

  Set oEdiDoc = New Fredi.ediDocument
  

• Load the schema.

  Dim oSchemas As Fredi.ediSchemas
  Dim oSchema As Fredi.ediSchema
  
  ' Disable standard reference library.
  Set oSchemas = oEdiDoc.GetSchemas
  oSchemas.EnableStandardReference = False
  
  Set oSchema = oEdiDoc.LoadSchema(App.Path & "\SampleAscX12_850.SEF", Schema_Standard_Exchange_Format)

• Load the document.

  ' Load EDI document normally.
  oEdiDoc.LoadEdi App.Path & "\SampleEdiX12_850.X12"
  
  

• Get the first interchange.

  Dim oInterchange As Fredi.ediInterchange
  
  ' Get first interchange.
  Set oInterchange = oEdiDoc.FirstInterchange
  
  

• Get the interchange header and read elements

  ' Get interchange header.
  Dim oHeader As Fredi.ediDataSegment
  Dim oElements As Fredi.ediDataElements
  Dim oElement As Fredi.ediDataElement
  Dim sResult As String
  Dim i As Integer
  
  Set oHeader = oInterchange.GetDataSegmentHeader
  
  ' Get elements collection.
  Set oElements = oHeader.DataElements
  
  sResult = ""
  
  For Each oElement In oElements
  

  sResult = sResult & oElement.ID & " = " & oElement.Value & vbCrLf
  

  
  Next
  

Programmatically Generating the Interchange Header

The following steps demonstrates how to generate the interchange header.

• Create an instance of ediDocument.

  Dim oEdiDoc As Fredi.ediDocument

  Set oEdiDoc = New Fredi.ediDocument
  

• Load the schema.

  Dim oSchemas As Fredi.ediSchemas
  Dim oSchema As Fredi.ediSchema
  
  ' Disable standard reference library.
  Set oSchemas = oEdiDoc.GetSchemas
  oSchemas.EnableStandardReference = False
  
  Set oSchema = oEdiDoc.LoadSchema(App.Path & "\SampleAscX12_850.SEF", Schema_Standard_Exchange_Format)

• Specify the terminators.

  ' Specify the terminators to use on the document.
  oEdiDoc.SegmentTerminator = vbCrLf
  oEdiDoc.ElementTerminator = "*"
  oEdiDoc.CompositeTerminator = ">"
  
  

• Create the interchange.  The CreateInterchange method creates the interchange entity including the interchange header and trailer control segment.

  Dim oInterchange As Fredi.ediInterchange
  
  ' Create the Interchange envelope.
  Set oInterchange = oEdiDoc.CreateInterchange("X", "005030")
  
  

• Set the values in the interchange header.

  Dim oHeader As Fredi.ediDataSegment
  
  ' Get the interchange header.
  Set oHeader = oInterchange.GetDataSegmentHeader
  
  ' Set the values of the elements.
  oHeader.DataElementValue(1) = "00"
  oHeader.DataElementValue(3) = "00"
  oHeader.DataElementValue(5) = "ZZ"
  oHeader.DataElementValue(6) = "SENDERISA"
  oHeader.DataElementValue(7) = "ZZ"
  oHeader.DataElementValue(8) = "RECEIVERISA"
  oHeader.DataElementValue(9) = "960807"
  oHeader.DataElementValue(10) = "1548"
  oHeader.DataElementValue(11) = "U"
  oHeader.DataElementValue(12) = "00503"
  oHeader.DataElementValue(13) = "000000020"
  oHeader.DataElementValue(14) = "0"
  oHeader.DataElementValue(15) = "T"
  oHeader.DataElementValue(16) = ">"