Mike Smith wrote:

> Which is the dilemma between selling multiple quantities of an
> identical item, and using the bar-code as a asset number.  Since ppl
> don't need to remember barcodes, why not add an extra, say, 128 bits
> at the manufacture stage, starting at 0 for every unique product.
> You wouldn't need to store the entire number, hashing it with the
> unique product number would do...

UPC effectively is what you just suggested. UPC is a quite a secure
bar-code method (Very difficult to get a wrong valid answer) It is a
well thought out industry driven standard. A lot of thought was put
into the kind of things that would be sold vs. the kind of things
that would be inventoried.

Library books are typical of one type
of inventory with multiple copies that each has to be handled
separately. Mr. Jones has a copy of the book that is overdue but
Mr. Smith is not overdue until next week. And the book's author
is Doe, J. W. and library has three copies two are currently out
the third is on the second floor. This problem has often been
solved in libraries using CODE39 with a unique number on each
book. Since CODE39 is a character oriented bar-code a inventory
number is machine generated which includes a check digit often
either a checksum or credit card type modulus. Libraries solve
the multiple use (whose got and what is it) is solved in a
very library fashion of many different cross indexes on the
inventory data base.

I2of5 is generally used as an inventory control where we
control what is in the inventory and we may three of an item
and we cannot tell the difference and don't care. Each item
type has a different number. The system has a master index.
An example is an automotive plant parts index. If you live
in North America the stickers on a new car are Iof5.

UPC is another inventory control type code that has a the
problem of being printed by many different printers and
on products that don't really like to be bar-coded. To
name three of the common problems, pop bottles where you
have white on black when the bottle is full and white on
clear when it is empty (or upside down). This code was
designed to be read with bars of both lighter or darker
contrast in the same context. It was designed to be read
in both directions with equal ease. The two remaining
problems are the ice-cream container very cold on a hot
day covered with frost and the un-frozen frozen vegetables.

UPC is an inventory control system where the supplier is
important and local product inventory pricing is important.
The supplier and general product area can be identified from
the code on a product. This information is useful in tracking
down information on a uninventoried product. There is enough
information to maintain a local inventory. UPC is compact
with good checking capability and easy to read in very bad
conditions. UPC is an industry controlled standard.

Walter Banks
http://www.bytecraft.com