ANSI X12 Manual Overview and Usage Guidelines

ANSI X12 Manual is the ultimate source for the EDI standards. It is a large thick book with over 1500 pages of EDI transaction-set, segment and data element references. ANSI X12 is also available on a CD-ROM in PDF format.

ANSI X12 reference manual can be purchased on the DISA.ORG website: The following (courtesy of DISA and ASC X12 Manual) are extracts from this manual in order to describe the formats of Transactions, Segments and Data Elements.

The following is an extract describing the format of the transaction set:


The following is an extract describing the format of a segment:


The following is an extract from the X12 manual of the PO1 segment:


A: This is the data element reference designator. It is just a sequential number. REF-03 can be referred to for the description.

B: This is the data element reference number. The element ID number can be used to look up all the details all about this element.

C: This is the name given to the data element. It should be descriptive enough to understand. For example, REF-03 = Description.

D: This is the requirement usage indicator and may contain the following:

  • O – Optional: The data element is optional. If trading partners choose, they can make this field mandatory in their implementation guidelines.
  • M – Mandatory: The element must appear in the segment. Trading partner implementation guidelines should not change the mandatory requirement to optional. Here is an example of a mandatory element from the BGN segment:


  • X – Conditional: The segment requirement depends on a conditional relationship. For example, if REF-02 Reference Identification is sent then REF-01 reference identification qualifier is mandatory.

E: This is the data type attribute:

  • AN – Alpha Numeric: This will typically contain letters and digits, although it can also handle spaces and special characters.
  • R – Decimal Number: This is a numeric value. If the value is an integer, decimal points should not be sent. Decimal points should be sent only for fractional values. Negative amounts can be sent with a minus sign “-“ in front of the number. The absence of the minus sign indicates a positive value.
  • N(n) – Numeric: This can have two positions. The first N is a numeric value and the second (n) is the number of decimal places to the right.
  • ID – Identifier: The data type is specified by the data element ID that it relates to. For example, REF-01 is the Reference Qualifier.
  • DT – Date: This is the date format. It can be either YYMMDD or CCYYMMDD in which CC is the century, YY is the year, MM is the month, and DD is the day.
  • TM – Time: This is the time format in a 24-hour clock format: HHMMSS – HH is the hour, MM is minute, and SS second.

F: This is simply the minimum and maximum length of the element. For example, if the REF-01 is being used. The minimum and maximum length of this element is 2/3. It has to be at least two characters (e.g. EA) and can not be greater than three characters.

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