WHAT are GTIN's and WHY are they so confusing?

Automatic Identification Data Capture (AIDC) technologies like bar codes and RFID,   consist of three parts:  data, data structure, and a data carrier.      The data is a globally unique number.  When using the EAN.UCC system, the data   structure includes an EAN/UCC company prefix, an item reference number and   a check digit.  The data carrier can be any one of several bar code symbologies or   an RFID chip.     Global Trade Item Numbers (GTIN) include the UCC-12, EAN-8, EAN-13   and EAN.UCC-14.     For an explanation of fourteen digit GTIN's, please see "Those Darn Zeros".     EAN.UCC rules determine which type of GTIN is carried in which type of bar code   symbol for each Package Level.
Types of GTIN's	Types of Bar Code Symbols	Package Levels
UCC-12	EAN/UPC
EAN-8	UCC / EAN 128	Standard Trade Item
EAN-13	Interleave 2 of 5	Retail Consumer Trade Item
EAN.UCC-14	Reduced Space Symbols
AND how it all works depends on what time it is!  See Sunrise 2005.

GTIN's made EASY
Start with the application (in North America):
Scanned at POS after 01/05?	Yes	UCC-12 or EAN-8 or EAN-13
Scanned at POS outside N. America?	Yes	UCC-12 or EAN-8 or EAN-13
Marking a standard carton, pallet,etc.?	Yes	UCC-12 or EAN-13 or EAN.UCC-14
Global Trade Items are:  UCC-12 or EAN-8 or EAN-13 or EAN.UCC-14
As always, there are exceptions: organic oranges, small syringes, thirteen   digits issued by the UCC....  BUT you people know who you are!