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<title>Date-Time Terminology</title>
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<link href="doxygen.css" rel="stylesheet" type="text/css">
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<a href="../../../index.htm">
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<img align="left" src="../../../c++boost.gif" alt="C++ Boost">
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<h1>Date-Time Terminology</h1>
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<p> <p>
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<hr>
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<a href="index.html">Overall Index</a> --
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<a href="gregorian.html">Gregorian Index</a> --
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<a href="posix_time.html">Posix Time Index</a>
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<p>
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<p>
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The following are a number of terms relevant to the date-time domain.
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<P>
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<P>A taxonomy of temporal types:
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<UL>
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<LI><B>Timepoint</B> -- Specifier for a location in the time continuum.
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Similar to a number on a ruler.
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<LI><B>Timelength</B> -- A duration of time unattached to any point on the
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time continuum.
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<LI><B>Timeinterval</B> -- A duration of time attached to a specific point in
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the time continuum. </LI></UL>
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<P>And some other terms:
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<UL>
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<LI><B>Accuracy</B> -- A measure of error, the difference between the reading
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of a clock and the true time.
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<LI><B>Calendar System</B> -- A system for labeling time points with day level
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resolution.
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<LI><B>Clock Device</B> -- A software component (tied to some hardware) that
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provides the current date or time with respect to a calendar or clock system.
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<LI><B>Precision</B> -- A measure of repeatability of a clock.
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<LI><B>Resolution</B> -- A specification of the smallest representable
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duration (eg: 1 second, 1 century) for a clock/calendar system or temporal
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type.
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<LI><B>Stability</B> -- The property of a class which says that the underlying
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representation (implementation) associated with a particular (abstract) value
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will never change.
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<LI><B>Time System</B> -- A system for labeling time points with higher
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resolution than day-level. </LI></UL>
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<P>Some standard date-time terminology:
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<UL>
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<LI><B>Epoch</B> -- Starting time point of a calendar or clock system.
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<LI><B>DST -- Daylight savings time</B> - a local time adjustment made in some regions during the summer to shift the clock time of the daylight hours
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<LI><B>Time zone</B> -- A region of the earth that provides for a 'local time'
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defined by DST rules and UT offset.
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<LI><B>UTC Time</B> -- Coordinated Universal Time - Civil time system as
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measured at longitude zero. Kept adjusted to earth rotation by use of leap
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seconds. Also known as Zulu Time. Replaced the similar system known as
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Greenwich Mean Time. For more see <A
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href="http://aa.usno.navy.mil/faq/docs/UT.html">http://aa.usno.navy.mil/faq/docs/UT.html</A>
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<LI><B>TAI Time</B> -- A high-accuracy monotonic (need better term) time
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system measured to .1 microsecond resolution by atomic clocks around the
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world. Not adjusted to earth rotation. For more see <A
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href="http://www.bipm.fr/enus/5_Scientific/c_time/time_server.html">http://www.bipm.fr/enus/5_Scientific/c_time/time_server.html</A>
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</LI></UL>
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<P>Some more experimental ones:
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<UL>
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<LI><B>Local Time</B> -- A time measured in a specific location of the
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universe.
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<LI><B>Time Label</B> -- A tuple that either completely or partially specifies
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a specific date-time with respect to a calendar or clock system. This is the
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year-month-day representation.
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<LI><B>Adjusting Time Length</B> -- A duration that represents varying
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physical durations depending on the moment in time. For example, a 1 month
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duration is typically not a fixed number of days and it depends on the date it
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is measured from to determine the actual length. </LI></UL>
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<P>These are design sorts of terms:
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<UL>
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<LI><B>Generation function</B> -- A function that generates a specific set of
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time points, lengths, or intervals based on one or more parameters. </LI></UL>
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<hr>
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<address><small>
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<!-- hhmts start -->
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Last modified: Sat Oct 26 08:37:53 MST 2002
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<!-- hhmts end -->
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by <a href="mailto:jeff@crystalclearsoftware.com">Jeff Garland</a> © 2000-2002
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</small></address>
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