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IUID:   Item Unique Identification (aka UID)

The UID in IUID stands for Unique Identification, which refers in a general sense to methods and systems for uniquely identifying things.  This idea gained traction within the aerospace and automotive industries as a way to ensure that equipment from different manufacturers and countries could be uniquely identified.   Adding a part number to a serial number makes the combined identifier more unique.  Further adding the manufacturer’s identifier and the country of origin makes it even more so.  
Most people may be unknowingly familiar with UIDs in the form of the Vehicle Identification Number, or VIN, attached to every car.   Each manufacturer assigns serial numbers to the automobiles they manufacturer.  But without a system to control these numbers there would be a lot of duplications, especially since everyone starts with one and counts from there.

The International Organization for Standardization (ISO) stepped in with a standard defining the VIN, which adds an ISO-assigned World Manufacturer ID and other attributes to the serial number to ensure that each is truly unique.   That’s why VINs are so long.

By 2004, the US Department of Defense (DOD) had adopted the system of Item Unique Identification (IUID) that was popular with the aerospace industries of NATO countries to achieve the same result for items other than vehicles.   Adding the manufacturers identifier (CAGE code or DUNS number) and item part number to serial numbers helps the DOD ensure that items are uniquely identified.   The result is a Unique Item Identifier (UII), which is permanently marked on each serial managed part purchased by the DOD and placed in a huge database called the UID Registry (or more properly, the IUID Registry).

Defense contractors must submit the UII of each item it is shipping to the Government’s Wide Area Workflow (WAWF) system prior to shipping, which in turn checks these UIIs in the IUID Registry.  Items found already to exist in the Registry are not accepted by the Government, thus helping to ensure that items are, in fact, uniquely identified.

Terminology

What is a UII (or IUID)?

For DoD Item Unique Identification, the UII is the string of up to 50 characters that uniquely identifies an item on a global scale. It includes at a minimum, the identifier of the entity that issued the UII and a sequence number.  Depending on the construct or methodology, more information may be included to enhance the usability of the UII.  At a minimum, the UII also includes a code that identifies the type of Entity Iidentifier used.

The DoD IUID system supports several methods of methodologies for building UIIs, based on specific needs and circumstances.   The two most prevalent are the Construct 1 and Construct 2.   Before defining them, it helps to understand their first two components.

UII Entity ID

The Entity ID (EID) is one of the things that keep identifiers unique.   Every defense contractor could assign a given serial number, say ‘00001’, which would hardly be unique.  However, adding their company ID in front of it, would do that, provided they issued one of every IUID serial number.  More about that later.   The three most popular Entity IDs are:

Issuing Agency Code (IAC)

The IAC identifies the agency that issued the Entity ID, shown in parentheses in the above list.   The IAC indicates what portion of the UII is the Entity ID.  For example, looking at the UII D1HLD9ABCDE000001, we recognize that the D indicates a CAGE code, and thus the next five characters are a CAGE code and the rest are part of the UII.  Conversely, UII LDX092H1ABCDE000001 indicates a UII belonging to DODAAC X09H1.

Construct 2 UII

A Construct 2 UII consists of four parts:

Construct 2 is commonly used, largely because it does not require any management of the serial number portion beyond what a company would already have in place to manage the serial numbers it assigns to parts.

Construct 1 UII

Construct 1 consists of a serial number that is issued by an entity that is unique across all items, rather than with regard to a specific part number.   

There at least a couple of reasons one might choose to use Construct 1:

The downside of Construct 1 is that the entity must have a system in place to manage the UII serial numbers and correlate them to parts and their serial numbers.   With Construct 2 one can determine the item’s part number by looking at the UII, and from that the item’s serial number.  And, they rely on the manufacturer’s existing serial number management systems to ensure uniqueness.

Data Matrix (2D) Symbol versus UII

UIIs appear in two forms, human-readable and machine-readable, although that distinction is a little blurred by use.  The 2D Data Matrix symbol includes delimiters that allows automated systems to determine that the symbol is an IUID and also determine the individual components of the symbol.  The term Machine-Readable Interface (MRI) refers to both the encoded UII and the data structure of the Data Matrix symbol as defined by Mil-Std-130N.

The UII is just the data without any encoding. The example below shows how delimiters and data identifiers in the Data Matrix’s MRI assist automated systems understand exactly the components of the UII encoded in the symbol.

    UII:   D1HLD9ABCDE000001

    MRI:    [)> RS 06 GS 17V 1HLD9 GS 1P ABCDE GS S000001 RS EOT

In the MRI, “[)>RS06” tells a reader to expect a machine-readable content that includes data identifiers in the stream, in this case a 17V (CAGE), 1P (part number) and S (serial number).

UIIs that appear without any encoding are referred to as Concatenated UIIs.   This is the form that UIIs are most often communicated in, such as when submitted to WAWF at time of acquisition.  However, WAWF still wants to know how the IUID may be broken down, so it requires that the serial number portion be communicated as well.

This is also true of IUIDs as found in the 2D PDF417 symbol that appears on the Mil-Std-129 Exterior Container Label, but in their Concatenated UII form, as indicated by the 25S Data Identifier.

     PDF417 UID:    ... GS 25S D1HLD9ABCDE000001 GS S 000001 ...

The UII is followed by its serial number component, indicated by the S data identifier. By knowing the serial number component and the IAC, one can determine if where the Entity ID ends and the Serial Number begins.   Anything in between would be the Part Number, making the UII a Construct 2.