RFC 1439 (rfc1439) - Page 2 of 11

The Uniqueness of Unique Identifiers

RFC 1439            Uniqueness of Unique Identifiers          March 1993


   and duplicates are handled in an ad-hoc manner.  Example identifiers
   are:

           Craig.Finseth
           caf

   Now that we have widespread electronic mail, an important feature of
   an identifier system is the ability to predict the identifier based
   on other information associated with the individual.  This other
   information is typically the person's name.

   Methods two and three make such predictions possible, especially if
   you have one example mapping from a person's name to the identifier.
   Method two relies on using some or all of the name and
   algorithmically varying it to ensure uniqueness (for example, by
   appending an integer).  Method three relies on using some or all of
   the name and selects an alternate identifier in the case of a
   duplication.

   For both methods, it is important to minimize the need for making the
   adjustments required to ensure uniqueness (i.e., an integer that is
   not 1 or an alternate identifier).  The probability that an
   adjustment will be required depends on the format of the identifer
   and the size of the organization.

2. Identifier Formats

   There are a number of popular identifier formats.  This section will
   list some of them and supply both typical and maximum values for the
   number of possible identifiers.  A "typical" value is the number that
   you are likely to run into in real life.  A "maximum" value is the
   largest number of possible (without getting extreme about it) values.
   All ranges are expressed as a number of bits.

2.1 Initials

   There are three popular formats based on initials: those with one,
   two, or three letters.  (The number of people with more than three
   initials is assumed to be small.)  Values:

           format                  typical         maximum

           I                       4               5
           II                      8               10
           III                     12              15






Finseth