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The process of identifying physical objects is such a fundamental part of our
experience that we seldom think about how we do it. We use our senses, of
course: we look at, feel, pick up, shake and listen to, smell, and taste objects
until we have a reference for them—then we give them a label. The whole
process relies on some pretty sophisticated work by our brains and bodies,
and anyone who’s ever dabbled in computer vision or artificial intelligence
in general can tell you that teaching a computer to recognize physical objects
is no small feat. Just as it’s easier to determine location by having a human
being narrow it down for you, it’s easier to distinguish objects computationally
if you can limit the field, and if you can label the important objects.
Just as we identify things using information from our senses, so do computers.
They can identify physical objects only by using information from
their sensors. One of the best-known digital identification techniques is radio
frequency identification, or RFID. The network identity of a physical object
can be centrally assigned and universally available, or it can be provisional.
It can be used only by a small subset of devices on a larger network or used
only for a short time. RFID is an interesting case in point. The RFID tag pasted
on the side of a book may seem like a universal marker, but what it means
depends on who reads it. The owner of a store may assign that tag’s number
a place in his inventory, but to the consumer who buys it, it means nothing
unless she has a tool to read it and a database in which to categorize it. She
has no way of knowing what the number meant to the store owner unless
she has access to his database. Perhaps he linked that ID tag number to the
book’s title or to the date on which it arrived in the store. Once it leaves the
store, he may delete it from his database, so it loses all meaning to him. The
consumer, on the other hand, may link it to entirely different data in her own
database, or she may choose to ignore it entirely, relying on other means to
identify it. In other words, there is no central database linking RFID tags and
the things they’re attached to, or who’s possessed them.
Like locations, identities become more uniquely descriptive as the context
they describe becomes larger. For example, knowing that my name is Tom
doesn’t give you much to go on. Knowing my last name narrows it down some
more, but how effective that is depends on where you’re looking. In the United
States, there are dozens of Tom Igoes. In New York, there are at least
three. When you need a unique identifier, you might choose a universal label,
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