[from The Year 2000 and 2-Digit Dates: Guide
(C) Copyright IBM Corp. 1995, 1996]

  This glossary defines data                CENTURY.  A period of 100
  processing and communication terms        consecutive years.
  used in this publication.
                                            Although IBM recognizes that the
                                            21st century begins at 0000 hrs, 1
     +----------+                           January 2001, for purposes of this
     | NUMERICS |                           document, we are defining the
     +----------+                           20th--21st century boundary to be
                                            between 2400 hrs, 31 December
  2-DIGIT-YEAR FORMAT.  A format that       1999 and 0000 hrs, 1 January 2000.
  provides a year date as two digits        This allows a discussion of the 21st
  only to represent a year within a         century to include all dates with a
  specific century.  The two                20yy format inclusive of the year
  high-order digits of the year are         2000.  Hence, the year 2100 is
  truncated; for example "1995" is          likewise relegated to the 22nd
  represented as "95", and "00"             century.
  represents years ..."1800", "1900",
  "2000"....                                CENTURY BYTE.  The high order byte
                                            of a field used to contain the two
  4-DIGIT-YEAR FORMAT.  A format that       high order digits of a 4-digit year.
  provides a year date as four digits:      (For example, 19 in 1995, 20 in 2000
  the two high-order digits represent       and 2001).
  the century and the two low-order
  digits represent the year within the      COSMETIC.  Referring to a
  century.  For example, "1995"             2-digit-year date that is viewed by
  represents the year 1995; "2095"          human eyes only, such as a print
  represents the year "2095".               date on hardcopy output or a date on
                                            a selection panel.  Because it is
                                            neither read nor further processed
     +---+                                  by a program you might be able to
     | C |                                  exclude its modification from your
     +---+                                  year2000 work effort.
  CCYY FORMAT.  A 4-digit-year format
  that uses two century digits (CC) to         +---+
  indicate the century and two year            | E |
  digits (YY) to indicate the year             +---+
  within the century.  The CC
  representation is provided as either      EXTERNAL SIDE.  The receiver of a
  the actual century digits (for            data entity.  Used in this document
  example, 18, 19, or 20) or as a           to mean a module or routine that
  encoded value (for example, as 00 to      accepts a 2- or 4-digit-date format
  represent 19, 01 to represent 20 as       entity for further processing from
  in, "0095" represents the year            another module or routine.
  "1995" and "0195" represents the
  year "2095".)
     +---+                                     +---+
     | F |                                     | L |
     +---+                                     +---+
  FIXED WINDOW.  A technique to             LEAP YEAR.  A year either evenly
  determine the century (high-order         divisible by 400 OR evenly divisible
  digits) of a year when represented        by 4 and not evenly divisible by
  by two digits.  The 2-digit year is       100.  For example, the year 1900 was
  compared against a hardcoded              not a leap year but the year 2000 is
  threshold.  The century designation       a leap year.
  is limited to a 100-year range
  spanning only two centuries.  For         LILIAN DATE.  The number of days
  example, assume the threshold is 60,      since 14 October 1582.  15 October
  then if the 2-digit year is 60, the      1582 is Lilian day 1, 16 October
  year is in the 20th century; if the       1582 is Lilian day 2, and so on.
  2-digit year is <60, the year is in       (Named for Aloysius Lilius (an
  the 21st century.                         advisor to Pope Gregory XIII) who,
                                            together with his brother,
                                            constructed the current Gregorian
     +---+                                  calendar.)
     | G |
  GREGORIAN CALENDAR.  Today's                 | R |
  general-use calendar of 12 months            +---+
  and 365 days that employs the
  current leap year algorithm (refer        ROLLING WINDOW.  Synonymous with
  to LEAP YEAR below).                      SLIDING WINDOW.
     +---+                                     +---+
     | I |                                     | S |
     +---+                                     +---+
  INTERNAL SIDE.  The creator or            SLIDING WINDOW.  A technique to
  manipulator of a data entity.  Used       determine the century (high-order
  in this document to mean a module or      digits) of a year when represented
  routine that externalizes a 2- or         by two digits.  The user specifies
  4-digit-year format entity to             the number of years (both past and
  another module or routine.                future) within a 100-year window
                                            spanning two centuries.  For
                                            example, assume the window is set at
     +---+                                  19 future years (1996-2014) and 80
     | J |                                  past years (1915-1994).  Dates in
     +---+                                  the range "00-14" (inclusive) are
                                            designated 21st century dates
  JULIAN DATE.  A date in the format        because they fall into the future
  YYDDD.  A date format that contains       window.  Dates in the range "15-99"
  the year in positions 1 and 2, and        (inclusive) fall into the 20th
  the day in positions 3 through 5.         century.
  The day is represented as 1 through
  366, right adjusted, padded with
  zeroes on the left.
     +---+                                  YEAR2000 READY.  The capability of a
     | T |                                  software program to correctly
     +---+                                  interpret and manipulate year-date
                                            data outside the 1900-1999 year
  TRANSFORMATION 2000.  IBM's               range and produce valid arithmetic
  Information Systems Solution              results.
  Corporation (ISSC) comprehensive set
  of solutions that takes into account      YEAR2000 TRANSITION.  The process of
  applications, systems software and        revising all programming entities
  hardware in both a centralized            (programs, databases, and so on) to
  and/or distributed environment.           correctly process date data outside
                                            the range 1900-1999.
     +---+                                  YY FORMAT.  Synonymous with
     | Y |                                  2-DIGIT-YEAR FORMAT.
                                            YYYY FORMAT.  Synonymous with
  YEAR2000 CHALLENGE.  The work-effort      4-DIGIT-YEAR FORMAT and a subset of
  required to complete a Year2000           CCYY FORMAT.
  transition, to include planning,
  identifying, reformatting, testing,
  and migrating phases.                        +----------+
                                               | NUMERICS |
  YEAR2000 PROBLEM.  The potential             +----------+
  problems and its variations that
  might be encountered in any level of      20TH CENTURY.  The period of time
  computer hardware or software from        0000.00 hrs 1 January 1901 through
  microcode to application programs,        2400.00 hrs 31 December 2000.
  files, and databases that need to
  correctly interpret year-date data        21ST CENTURY.  The period of time
  represented in 2-digit-year format.       0000.00 hrs 1 January 2001 through
                                            2400.00 hrs 31 December 2100.

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