A GDTI is formed with the following components:
- APPLICATION IDENTIFIER (AI): AI (253) to indicate GDTI
- GS1 COMPANY PREFIX: A globally unique number allocated to a GS1 member company
- DOCUMENT TYPE: The number assigned to identify the type of document
- CHECK DIGIT: A modulo-10 check digit used to check for input errors
- SERIAL NUMBER: An optional alpha-numeric identification for individual document

The following steps are used to form GDTIs:
- Start with your GS1 company prefix
Your GS1 Company Prefix is the globally unique number allocated to your company by GS1 Australia or another GS1 Member Organisation.
- Create the document type
The Document Type is a number assigned by you, the holder of the GS1 Company Prefix, to uniquely identify a type of document within your company. The Document Type varies in length as a function of the GS1 Company Prefix length. Note that the combined length of the GS1 Company Prefix and Document Type is always 12 digits.
Hint: Assign your Document Types sequentially, and do not build any intelligence into the number. The scheme that defines a particular document type range as having a set meaning today will mean nothing a short time into the future when your company reorganizes, buys or merges with another firm, or another staff member takes over GDTI assignment duties.
- Calculate the check digit
The Check Digit is a calculated one-digit number used to ensure data integrity. Find out how this digit is calculated.
4. (Optional) assign the serial number: The serial number gives you the option of tracking not only specific document types, but also specific instances of each document type (i.e., not just a land registration document, but this specific land registration document). You can assign up to a 17- character alpha-numeric serial number for each GDTI. Again, we recommend assigning serial numbers sequentially, not building any type of intelligence into the serial number itself.