ISO
8601:2000(E)
©
ISO
2000
All
rights
reserved
5
3.29
year
unit
of
time
of
which
the
duration
equals
the
duration
of
a
calendar
year
3.30
year,
calendar
cyclic
time-interval
in
a
calendar
which
is
required
for
one
revolution
of
the
earth
around
the
sun
(approximated
to
an
integral
number
of
calendar
days)
NOTE
A
calendar
year
is
often
also
referred
to
as
year.
3.31
year,
centennial
á
Gregorian
calendar
ñ
calendar
year
whose
year
number
is
divisible
by
hundred
an
integral
number
of
times
3.32
year,
common
á
Gregorian
calendar
ñ
calendar
year
that
has
365
days
3.33
year,
leap
á
Gregorian
calendar
ñ
calendar
year
that
has
366
days
NOTE
The
rules
used
for
assigning
the
extra
day
are
given
in
4.3.2.1.
4
Fundamental
principles
4.1
Basic
concepts
For
the
purpose
of
this
International
Standard,
four
concepts
are
fundamental:
¾
Time-point
:
an
instant
in
the
laps
of
time
regarded
as
dimensionless.
Time-points
are
determined
by
specifying
their
position
(i.e.
their
'distance'
in
time
from
the
zero-point)
in
a
time
oriented
reference
system.
¾
Time-interval
:
a
portion
of
time
between
two
time-points.
These
time-points
are
respectively
labelled
"start"
and
"end".
Time
intervals
may
be
specified
by
these
two
time-points,
by
one
of
these
time-points
and
the
temporal
distance
between
the
points
or
by
the
temporal
distance
between
these
points
only.
¾
Recurring
time-interval
:
a
series
of
consecutive
time-intervals
of
the
same
duration.
Recurring
time-intervals
may
be
specified
by
specification
of
one
time-interval
and
the
number
of
recurrences.
¾
Duration
:
a
quantity
("length")
of
time.
Duration
is
a
physical
unit
expressed
in
the
units
of
time
of
the
International
System
of
Units
(SI),
as
defined
in
ISO
31-1.
Both
precise
and
approximate
time-points
and
time-intervals
can
be
identified
by
means
of
unique
and
unambiguous
expressions
specifying
the
relevant
dates
and
times
of
the
day.
This
International
Standard
specifies
a
set
of
rules
for
the
representation
of
dates,
times-of-the
day,
time-intervals
and
recurring
time-intervals.
The
degree
of
precision
required
and
obtainable
can
be
varied
by
including
or
deleting
the
appropriate
time
elements
(such
as
seconds).
4.2
Common
features,
uniqueness
and
combinations
The
decreasing
order
of
components,
left-to-right,
is
common
to
the
expressions
for
¾
points
in
time;
¾
dates
only;
