Well, we have reached one of the limits of the metaphor.
Computer systems are much pickier than bartenders (or wine
sellers), and the reasons and business models that require online
identi?¬?cation are much more complex than our canonical
example.
Consider for a moment every home-banking application up and
running on the Internet today. Nearly every one of those applications,
and the corresponding back end, has a construct that
represents the concept of an account number. The semantic of
an account number is fairly unambiguous, even if some local
shades of meaning are possible. Yet the representations will
greatly vary from bank to bank. If you were to make those
home-banking applications participate in the Identity
Metasystem, their natural role would be an RP. The policy of
those RPs may state that the subject??™s identity should contain an
account number; however, because we are talking about computer
systems, the way in each bank indicates an account number
will make a difference. For the bartender, the DOB (Date of
Birth) ?¬?eld on the driver??™s license is happily equivalent to the
???Birth Date??? ?¬?eld on the passport; for a computer system,
AccountNumber is very different from Account_Number.
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