The Uniqueness of Unique Identifiers
RFC 1439

Document Type RFC - Informational (March 1993; No errata)
Last updated 2013-03-02
Stream Legacy
Formats plain text pdf html bibtex
Stream Legacy state (None)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state RFC 1439 (Informational)
Telechat date
Responsible AD (None)
Send notices to (None)
Network Working Group                                         C. Finseth
Request for Comments: 1439                       University of Minnesota
                                                              March 1993

                  The Uniqueness of Unique Identifiers

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard.  Distribution of this memo is
   unlimited.

Abstract

   This RFC provides information that may be useful when selecting a
   method to use for assigning unique identifiers to people.

1. The Issue

   Computer systems require a way to identify the people associated with
   them.  These identifiers have been called "user names" or "account
   names."  The identifers are typically short, alphanumeric strings.
   In general, these identifiers must be unique.

   The uniqueness is usually achieved in one of three ways:

   1) The identifiers are assigned in a unique manner without using
   information associated with the individual.  Example identifiers are:

           ax54tv
           cs00034

   This method was often used by large timesharing systems.  While it
   achieved the uniqueness property, there was no way of guessing the
   identifier without knowing it through other means.

   2) The identifiers are assigned in a unique manner where the bulk of
   the identifier is algorithmically derived from the individual's name.
   Example identifers are:

           Craig.A.Finseth-1
           Finseth1
           caf-1
           fins0001

   3) The identifiers are in general not assigned in a unique manner:
   the identifier is algorithmically derived from the individual's name

Finseth                                                         [Page 1]
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                                                         [Page 2]
RFC 1439            Uniqueness of Unique Identifiers          March 1993

   You can also think of these as first, middle, and last initials:

           I                       4               5
           F L                     8               10
           F M L                   12              15

2.2 Names

   Again, there are three popular formats based on using names: those
   with the first name, last name, and both first and last names.
   Values:

           format                  typical         maximum

           First                   8               14
           Last                    9               13
           First Last              17              27

2.3 Combinations

   I have seen these combinations in use ("F" is first initial, "M" is
   middle initial, and "L" is last initial):

           format                  typical         maximum

           F Last                  13              18
           F M Last                17              23
           First L                 12              19
           First M Last            21              32
Show full document text