Take, for example, unit doses of medicine, typically packaged in blister packs that can be as small as 0.75 inches (19 mm) on a side. The FDA wants the National Drug Code in bar code on these blisters (in EAN.UCC format). When you consider all the FDA-mandated text that also has to be squeezed into this space, it's obvious that this is a space-constrained application just to accommodate a single bar code.
At the other end of the spectrum, the U.S. Department of Defense (DoD) requires a lot of information in machinereadable code on each shipping container. For smaller units, a label with all this data in conventional bar codes might be larger than the carton to which it's applied. So this, too, is a space-constrained application.
A third example that will soon impact a lot of companies is bar code backup for RFID tags. One suggestion is to include the 96-bit EPC data string in machine readable—whether a type of two-dimensional (2D) bar code or matrix symbol—in addition to currently mandated bar codes such as a 14-digit EAN.UCC Global Trade Item Number (GTIN) or 18-digit Serial Shipping Container Code (SSCC-18).
This third example perfectly illustrates "space-constrained" applications: any application where conventional, linear bar codes and required human-readable will not physically or economically fit on the item. The "physically" is easy to understand. But "economically" is a bit less obvious—unless you're responsible for buying label stock.
Despite the initial assumptions that a GTIN would be sufficient for most applications—to simply identify the product—and, when it wasn't, an SSCC-18 could serve as a pointer to a database, there is increasing interest in seeing more and more information on the label itself.
Where a product number might have been sufficient in the past, now lot/batch and expiration/best-by date are being considered to facilitate product recalls in food, pharmaceuticals and even consumer goods.
More bar codes equals more space. So what happens to a standard four by six inch (10 x 15 cm) shipping label that's already filled with bar codes and text? There are two possible answers: make the label larger or reduce the space required for bar code data.
The DoD recognized this practical consideration and mandated the use of PDF417 2D bar code to enable suppliers to meet its data requirements. For primary data (product ID), EAN.UCC developed a very efficient family of linear bar codes, Reduced Space Symbology (RSS) for marking of pharmaceuticals and other healthcare products. EAN.UCC also recognized Data Matrix 2D matrix symbology as an alternative when even the smallest RSS symbol would not fit.
These examples tend to represent the extreme ends of space-constrained applications: very large data requirements or extremely small physical space.
It is for the other type of constrained applications—the economic constraints—that there was a need to accommodate secondary data such as lot/batch and expiry/best-by date. EAN.UCC developed composite symbols made up of an UCC/EAN-128 or RSS linear symbol with an additional 2D component (a variation of PDF417), typically on top of the linear symbol. Inherent in this configuration is linkage between the linear symbol and the 2D component that tells a properly programmed reader that this is a composite symbol and that the data from the 2D component must be associated with the data from the linear component. Other industries, such as electronics and aerospace, opted for Data Matrix because of its greater print tolerances.
With a number of viable approaches for space-constrained marking, it's not safe to assume that any of them will be acceptable downstream. One company decided to "embrace the future" a bit too far ahead of the curve and replaced its existing U.P.C. symbols with RSS symbols—only to discover that none of its customers' scanners could read RSS. Here's one situation where the solution may be more problematic than the initial problem.