The Year 2000 and 2-Digit Dates: Guide
APPENDIX D.
GLOSSARY
This glossary defines data encoded value (for example, as 00 to
processing and communication terms represent 19, 01 to represent 20 as
used in this publication. in, "0095" represents the year
"1995" and "0195" represents the
year "2095".)
+----------+
| NUMERICS | CENTURY. Although IBM recognizes
+----------+ that the 21st century begins at 0000
hrs, 2001-January-01, for purposes
2-DIGIT-YEAR FORMAT. A format that of this document, we are defining
provides a year date as two digits the 20th--21st century boundary to
only to represent a year within a be between 2400 hrs,
specific century. The two 1999-December-31 and 0000 hrs,
high-order digits of the year are 2000-January-1. This allows a
truncated; for example "1995" is discussion of the 21st century to
represented as "95". include all dates with a 20yy format
inclusive of the year 2000. Hence,
4-DIGIT-YEAR FORMAT. A format that the year 2100 is likewise relegated
provides a year date as four digits: to the 22nd century.
the two high-order digits represent
the century and the two low-order CENTURY BYTE. The high order byte
digits represent the year within the of a field used to contain the two
century. For example, "1995" high order digits of a 4-digit year.
represents the year 1995; "2095" (For example, 19 in 1995, 20 in 2000
represents the year "2095". and 2001).
20TH CENTURY. The period of time COSMETIC. Referring to a
0000.00 hrs 1901-January-1 through 2-digit-year date that is viewed by
2400.00 hrs 2000-December-31. human eyes only, such as a print
date on hardcopy output or a date on
21ST CENTURY. The period of time a selection panel. Because it is
0000.00 hrs 2001-January-1 through neither read nor further processed
2400.00 hrs 2100-December-31. by a program you might be able to
exclude its modification from your
Year2000 work effort.
+---+
| C |
+---+ +---+
| E |
CCYY FORMAT. A 4-digit-year format +---+
that uses two century digits (CC) to
indicate the century and two year EXTERNAL SIDE. The receiver of a
digits (YY) to indicate the year data entity. A module or routine
within the century. The CC that accepts a 2- or 4-digit-date
representation is provided as either format entity for further processing
the actual century digits (for from another module or routine.
example, 18, 19, or 20) or as an
4-digit-year format entity to
another module or routine.
+---+
| F |
+---+
FIXED WINDOW. A technique to +---+
determine the century (high-order | J |
digits) of a year when represented +---+
by two digits. The 2-digit year is
compared against a hardcoded JULIAN DATE. As a general term used
threshold. The century designation widely in computer programming and
is limited to a 100-year range this document: A date in the format
spanning only two centuries. For YYDDD. A date format that contains
example, assume the threshold is 60, the year in positions 1 and 2, and
then if the 2-digit year is r60, the the day in positions 3 through 5.
year is in the 20th century; if the The day is represented as 1 through
2-digit year is <60, the year is in 366, right adjusted, padded with
the 21st century. zeroes on the left. For example,
1996-August-29 is 96242.
+---+ However, the above definition is
| G | accurately referred to as the
+---+ ORDINAL DAY OF YEAR date, and an
accurate definition of JULIAN DAY
GREGORIAN CALENDAR. Today's NUMBER is as follows:
general-use calendar of 12 months
and 365 days that employs the The astronomal system that counts
current leap year algorithm (refer the days since the First of January
to LEAP YEAR below). in the year 4713 BCE (the year -4712
before the common era). This scheme
was invented by the astronomer
+---+ Joseph Scaliger in the 16th century
| I | and named by him for his father
+---+ Julius. The leap year reforms
implicit in the new scheme were
INTEGER DATE. A count of days since adopted at the command of Pope
a specified date. Various IBM Gregory XIII in the year 1582 -
software products have defined hence the Gregorian Calendar. The
integer dates as follows: Gregorian, or New Style, calendar
was adopted in Britain and their
LANGUAGE/PRODUCT DAYS SINCE colonies in September of 1752.
(September of that year was missing
C 1969-Dec-31 11 days. The 14th followed the
2nd.)
COBOL 1600-Dec-31
The remainder left when dividing the
LANGUAGE ENVIRONMENT 1582-Oct-14 Julian Day Number by 7 indicates the
day of week of the specified date.
MVS/CICS/DB2 1899-Dec-31 Zero corresponds to Monday, 1 to
Tuesday, up through 6 for Sunday.
INTERNAL SIDE. The creator or
manipulator of a data entity. Used For example, 1996-Aug-29 is
in this document to mean a module or equivalent to Julian Day 2450325.
routine that externalizes a 2- or Further, the hour of the day is
expressed as a decimal such that
2450325.5 is midnight 1996-Aug-29, spanning two centuries. For
based on the fact that a Julian Day example, assume the window is set at
begins at mid-day (noon). 19 future years (1996-2014) and 80
past years (1915-1994). Dates in
the range "00-14" (inclusive) are
+---+ designated 21st century dates
| L | because they fall into the future
+---+ window. Dates in the range "15-99"
(inclusive) fall into the 20th
LEAP YEAR. A year either evenly century.
divisible by 400 OR evenly divisible
by 4 and not evenly divisible by SOLUTION DEVELOPERS. Also known as
100. For example, the years 1700, THIRD-PARTY VENDORS and INDEPENDENT
1800, 1900, and 1995 are not leap SOFTWARE VENDORS. Marketers of
years, but the years 1600, 1996, and computer hardware and/or software
2000 are leap years. products, tools, or services to
complement IBM's suite of products
LILIAN DATE. The number of days and services.
since 1582-October-14.
1582-October-15 is Lilian day 1,
1582-October-16 is Lilian day 2, and +---+
so on. (Named for Aloysius Lilius | Y |
(an advisor to Pope Gregory XIII) +---+
who, together with his brother,
constructed the current Gregorian YEAR2000 CHALLENGE. The potential
calendar.) problems and its variations that
might be encountered in any level of
computer hardware or software from
+---+ microcode to application programs,
| O | files, and databases that need to
+---+ correctly interpret year-date data
represented in 2-digit-year format
ORDINAL DAY OF YEAR. See JULIAN caused by the transition to the year
DATE 2000.
YEAR2000 READY. The capability of a
+---+ Product, when used in accordance
| R | with its associated documentation,
+---+ to correctly process, provide and/or
receive date data within and between
ROLLING WINDOW. Synonymous with the 20th and 21st centuries,
SLIDING WINDOW. provided that all products (for
example, hardware, software, and
firmware) used with the Product
+---+ properly exchange accurate date data
| S | with it.
+---+
YEAR2000 SUPPORT. The ability to
SLIDING WINDOW. A technique to provide YEAR2000 READINESS.
determine the century (high-order
digits) of a year when represented YEAR2000 TRANSITION. The process of
by two digits. The user specifies revising systems and databases) to
the number of years (both past and correctly process date data both
future) within a 100-year window
within and between the 20th and 21st YYYY FORMAT. Synonymous with
centuries. 4-DIGIT-YEAR FORMAT and a subset of
CCYY FORMAT.
YY FORMAT. Synonymous with
2-DIGIT-YEAR FORMAT.