Bar coding is an automatic identification technology that allows data to be collected rapidly and accurately with minimal human effort. Because of these attributes, bar coding has been used for a wide range of applications in almost every aspect of business. Bar codes provide a simple method of encoding text information that can be easily read by electronic scanners integrated with computer systems.
A simple bar code consists of a series of parallel, adjacent bars and spaces. These predefined bar and space patterns, or symbologies, are used to code character data into a standard, machine-readable format. Most bar-code symbologies can be scanned from at least two directions, which makes them easier and faster to scan, and more advanced ones can be scanned from nearly any angle. The basic structure of a bar code consists of a leading and trailing quiet zone, a start pattern, one or more data characters, one or two optional check characters, and a stop pattern.
A bar-code reader works by scanning a dot of light across a bar code symbol. As the dot scans the bar code, light is reflected back to the bar-code reader by the light areas and is absorbed by the dark areas. The scanner electronically measures the intensity of the reflected light to produce a digitized waveform that can be decoded back to the original message. Factors influencing the readability of a bar code include adequate contrast between the light and dark bars; all bar and space dimensions within the tolerances for the symbology; sharp bar edges; few or no spots or voids; a smooth surface; and clear margins or quiet zones at either end of the printed symbol.
Bar-code scanners come with different resolutions to enable them to read differently sized bar codes. The scanner's resolution is measured by the size of the dot of light, which must be equal to, or slightly smaller than, the narrowest element width (the "X" dimension). If the dot is wider than the width of the narrowest bar or space, then the scanner may become confused because of the dot's overlapping two or more bars at a time. If the dot is too small, then any spots or voids in the bars may be misinterpreted as light areas, rendering a bar code unreadable. To avert misreadings from any cause, many manufacturers and packagers submit their bar codes to electronic verification before they are released.
First utilized in supermarkets and libraries, bar coding has grown over the years to have applications in many fields. It is useful in almost any field that requires unique identification and tracking of a large number of items.
Bar-code technology is perhaps best known for its use in retailing for price verification and inventory control, but it is widely used throughout industry. Examples of other uses:
Bar codes take on many forms, and by some estimates there are more than 200 different formats available. However, only a dozen or so of these are widely used. Which standard a business chooses depends heavily on its industry and the nature of the information it needs to track. Many industries have de facto standards for bar codes, and the various bar code symbologies have vastly different capabilities, ranging from serial-number storage to the encoding of a diverse number of facts about an object. The following are summaries of some of the leading symbologies.
Universal Product Codes (UPCs) are used principally in retail. UPC-A, a 12-digit numeric symbology, consists of 11 data digits and 1 check digit. The first digit is a number-system digit that usually represents the type of product being identified. The next 5 digits are a manufacturer's code, and the following 5 digits are used to identify a specific product. UPCs are also emblazoned on manufacturers' coupons, with the last 3 of the second set of 5 digits sometimes indicating the monetary value of the discount; when the vendor coupon is scanned, the amount of the discount is automatically deducted from the customer's bill, and misredemption is minimized. UPCs are assigned to specific products and manufacturers by the Uniform Code Council (UCC), which manufacturers must join in order to use UPC codes.
UPC-E, a smaller, 6-digit UPC symbology for number system 0, is often used for small retail items. UPC-E is also called "zero-suppressed" because UPC-E compresses a normal 12-digit UPC-A code into a 6-digit code by "suppressing" the number-system digit, trailing zeros in the manufacturer's code, and leading zeros in the product-identification part of the bar code. A seventh check digit is encoded into a parity pattern for the 6 main digits. Thus, UPC-E may be uncompressed into a standard UPC-A 12-digit number. Both UPC-A and UPC-E allow for a supplemental two- or five-digit number to be appended to the main bar code symbol. Designed for use on publications and periodicals, the supplemental is simply a small additional bar code placed on the right side of a standard UPC symbol. This enables more detailed information about the product to be stored and captured.
Two international versions of the UPC, the European Article Number (EAN) and the Japanese Article Number, are similar to the UPC system in many respects. Analogous to UPC-E, EAN-8 stores eight numeric digits as follows: two country code digits, five data digits, and one check digit.
The full EAN-13, similar to UPC-A, differs mainly in that it includes a 13th digit to signify the country in which the product originated. The extra digit on the left-hand side of the code works in tandem with another digit to represent a country code. Both EAN-8 and EAN-13 allow an optional two- or five-digit number to supplement the main code. Designed for use on publications and periodicals, the Supplemental is simply an extra bar code appended to the right side of a standard EAN symbol. EANs are assigned to specific products and manufacturers through 87 regional numbering organizations that are all part of EAN International, a nonprofit association headquartered in Brussels, Belgium.
EAN-13 is adopted as the standard in the publishing industry for encoding the International Standard Book Number (ISBN) on books. An ISBN bar code is simply an EAN-13 symbol consisting of the ISBN number preceded by the digits 978. The supplemental message in an ISBN bar code is the retail price of the book preceded by a code for the currency in which the price is quoted. For example, if the ISBN number were 1-2345-6789-2 and the price of the book were US$22.95, then the main bar code would represent 978123456789 and the supplemental would encode 52295 (where the leading 5 indicates U.S. dollars). Mass-market novels sold in U.S. drug and grocery stores are one exception to the book standard; these use the UPC system because it is more compatible with the retailers' other bar-coding needs.
Widely implemented outside of retailing, Code 39 comes in two versions: normal, with a 44character capacity, and full ASCII, with a 128-character capacity. All Code 39 bar codes may be variable in length, allowing users substantial freedom to customize the codes to their specific needs. Indeed, multiple Code 39 symbols may be scanned in succession to create an extended message. The system also permits users to include check characters in their bar codes to help validate code integrity. Such flexibility has given Code 39 a large base of users in automotive manufacturing, health-care administration, and defense, among other applications. Since the 1980s the U.S. Department of Defense has required many of its contractors to supply Code 39 labeling on merchandise it purchases.
Used by the U.S. Postal Service to encode ZIP code information for automatic mail sorting by ZIP code, POSTNET, which stands for Postal Numeric Encoding Technique, encodes a 5-, 9-, or 11-digit number to indicate an item's destination. POSTNET can express a 5-digit ZIP code (32 bars), a 9-digit ZIP + 4 code (52 bars), or an 11-digit Delivery Point Code (62 bars). The POSTNET system uses a simple binary code represented by thin bars of fixed width but variable height. Short bars represent zero and tall bars represent one. This string of zeros and ones, then translates into the appropriate ZIP code or Delivery Point Code. This method was chosen by the U.S. Postal Service in 1976 because it could be printed on almost any type of printer and was easy to modify.
Facing Identification Marks (FIMs) are another type of bar code developed for automated mail processing. These are employed for automatic facing and canceling of mail that doesn't contain a stamp or meter imprint, such as business-reply mail. FIMs also serve to distinguish business-reply mail from other types.
Other common bar codes include the Codabar, the Interleaved 2 of 5 (1-2/5), the Discrete 2 of 5, Code 93, and Code 128. These are all high-density and variable-length symbologies, making them relatively compact and versatile. Some of these are standards in specific industries, for example, the Codabar in libraries. The first three, Codabar, 1-2/5, and Discrete 2 of 5, are essentially numeric-only codes, although the Codabar uses four alphabetic stop characters to separate streams of numbers. This allows several discrete pieces of information to be packed into one code. Code 93, an enhanced version of Code 39, allows one of the highest information densities available for alphanumeric characters; in other words, it requires the least space of the major alphanumeric symbologies. Code 128, on the other hand, permits users to encode not only alphabetic data, but also non-English characters.
Probably the most important area of new developments in bar coding is in the growth of two-dimensional (2-D) symbologies, including the PDF417 and many others. The advantages of 2-D codes over conventional linear ones are significant. They offer far greater information density, often can be scanned from any direction, and are much more resistant to damage because of elaborate error-handling capabilities. Because of such features, some observers have likened a 2-D code to an entire database of information about the object it is placed on.
Like many 2-D symbologies, PDF417 not only identifies the product, it also gives information about its source, destination, and proper handling. PDF stands for portable data file, a reference to the symbology's ability to store as many as 2,725 data characters—equivalent to more than 400 words—in a single code. As a result, one small square of a PDF417 code can contain as much information as a 20-foot strip of a linear code. PDF417 essentially consists of a stacked set of smaller bar codes, although it looks very different from a linear code. The PDF417 system includes such advanced features as data compression, error detection and correction, and variable size and aspect ratio symbols.
While PDF417 is known as a stacked symbology, MaxiCode is termed a matrix symbology because it is not read in rows. A matrix layout enables the code to be scanned from any direction and often achieves greater information density than any other format, including stacked symbologies. The fixed-size MaxiCode contains a primary and a secondary message, as well as two levels of error handling. Typical of matrix codes, this sophisticated system allows the code to function even if part of it has been damaged.
One of the most innovative uses of bar codes has nothing to do with tracking and identifying physical objects, but is instead concerned with the encryption of optical signals in telecommunications cables. In 1998 Commercial Technologies Corporation introduced fiber-optic communications technology that employs bar codes to encode rays of light as they pass through optical cable. This complex process creates an efficient and less expensive alternative to established fiber-optic transmission technologies, which require more network resources and external equipment to achieve the same effect of differentiating optical signals from one another. The end result is that communication network operators, such as telecommunications service providers, can add capacity more economically using the bar-code enhanced fiber-optic technology.
SEE ALSO : Automatic Identification Systems
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EAN International. EAN International Home Page. Brussels, Belgium, 1999. Available from www.ean.be .
Lindstrom, Annie. "Bar-Coding Fiber." America's Network, I July 1998.
TAL Technologies, Inc. "Bar Code Symbologies." Philadelphia, PA, 1997. Available from www.taltech.com .
Uniform Code Council, Inc. UCC: Home. Dayton, OH, 1999. Available from www.uc-council.org .