Another important concept in dealing with multiple bar coded fields on the label is Application Identifiers (AI) or Data Identifiers (DI). AI or DI is a specified character or set of characters within a bar code symbol, that defines the general category or specific use of the bar coded data that follows. The identifiers ensure proper validation of bar coded data. This is especially important when dealing with labels which contain multiple bar code fields and when using laser scanners as data entry devices. The identifiers ensure that only proper bar code fields from a label are scanned into relevant data entry fields on the PC or hand-held data entry screen. Two systems of identifiers are used:

Application Identifiers (AI) - These are defined by the UCC in the "Application specification for UCC/EAN-128 serial shipping container code" document. They are based on the UCC-128 symbology. Code UCC/EAN 128 (sometimes referred to as UCC -128) is an extended version of Code 128 capable of recognizing special starting sequences based on control characters such as FN1. These identifiers, in their human readable representation, are often visually separated from the rest of the data by brackets. The following are some examples of the use of Application Identifiers:

• Postal Code: (420) 98204 where "420" is the AI for the postal code and "98204" is the postal code
• Customer's Purchase Order Number: (400) 9602234-S where "400" is the AI for the Customer's Purchase Order Number and "9602234-S" is the Customer PO #
• Serial Shipping Container Code: (00) 1 0012345 123456789 5 where first "00" is the AI for the Serial Shipping Container Code (SSCC), "1" represents packaging type, "0012345" represents UCC assigned unique manufacturer / vendor ID code and the next group of digits represents vendor controlled shipping container serial number. The last digit ("5") is a control (check) digit.

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