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X12 Technical Tutorial - Overview


X12 is a U.S. standard and is primarily used in North America. The predominant international EDI standard is UN/EDIFACT. Accredited Standards Committee X12 of the American National Standards Institute (ANSI) is responsible for the X12 standard. For authoritative information on the standard, go to the source. Information on obtaining the standards may be obtained from the X12 Secretariat, the Data Interchange Standards Association.

Purpose of the Standards

The X12 standards provide structure for the electronic representation of business documents commonly exchanged between companies. Examples of such documents are Purchase Orders, Invoices, Shipment Notices, and Health Care Claims. Though some companies may use X12 formats internally between different applications or geographic locations, this usage is somewhat unusual. There are currently well over 300 documents defined in the standard.

The original idea behind a national standard for EDI is that having just one format for exchanging data would make exchange simpler. EDI evolved from one-on-one proprietary formats to industry formats. When it started being used by companies operating in several different trading communities, it became apparent that a cross-industry national standard was needed. The dream of a single, common format did not quite come to fruition. See the Implementation Issues page of this tutorial.

What the Standards Provide

The X12 standards provide a means to encode business documents so that they may be interpreted by a computer application. The documents are organized as delimited data, meaning data is separated by "delimiter" characters rather than by fixed length fields and records. The standards provide means to organize this data into business documents called Transaction Sets, group these into groups of related documents called Functional Groups, and wrap these in an envelope called an Interchange. The X12 standard has many parts, but the essential portions are:

  • X12.5 - Defines the structure of the Interchange, i.e., the ISA and IEA segments in the outer envelope
  • X12.6 - Defines the syntax for the standard. Defines data types, valid formats for a segment (a record), rules for organizing segments into Transaction Sets (documents), and grouping Transaction Sets into Functional Groups, or the GS/GE envelope.
  • Data Element Dictionary - Provide definitions of individual fields, or data elements. Provides the lowest level of semantics, or meaning.
  • Segment Dictionary - Provides definitions of records, or segments. Specifies the data elements which may occur in a segment. Provides the next level of semantics.
  • Transaction Set Tables - Provide the layouts of the individual business documents, specifying the particular segments which may occur in a Transaction Set. Provides the highest level of semantics.

The ASC X12 Committee and Versions of X12

The X12 committee meets three times a year to make further refinements to the standards. New documents, called Transaction Sets, may be developed. Minor enhancements to current Transaction Sets are also made to support the business needs of the members. This new development is incorporated into new releases of the standard. A major release is issued in December of each year, following the October X12 meeting. Subreleases are issued after the February and June meetings. New releases are intended to be backwardly compatible with old releases, i.e., software that can process an old version should be able to process a new version. However, this is not always the case.

Due to the frequent changes in the standard, specialized software, called EDI Translators, have developed to perform conversion from X12 formats into the internal formats used by companies.


The X12 standard in itself does not specify how the data should be transmitted between trading partners. Any computer-to-computer means will suffice, including magnetic tape. The most commonly used means is the use of a Value Added Network, or VAN. These VANs provide "mailbox" services, allowing a company to maintain only a single connection to the VAN with the VAN handling transmission to other companies (or their VANs), and collecting inbound transmissions. VANs may also provide services such as protocol conversion (I use Asynchronous Kermit and you use Bisynchronous 2780/3780), or character conversion (I use ASCII and you use EBCDIC).