<title>Infinite (Unbounded) Ranges</title>

<para>

The lower bound of a range can be omitted, meaning that all points less

than the upper bound are included in the range. Likewise, if the upper

bound of the range is omitted, then all points greater than the lower bound

are included in the range. If both lower and upper bounds are omitted, all

values of the element type are considered to be in the range.

The lower bound of a range can be omitted, meaning that all

values less than the upper bound are included in the range, e.g.,

<literal>(,3]</literal>. Likewise, if the upper bound of the range

is omitted, then all values greater than the lower bound are included

in the range. If both lower and upper bounds are omitted, all values

of the element type are considered to be in the range. Specifying a

missing bound as inclusive is automatically converted to exclusive,

e.g., <literal>[,]</literal> is converted to <literal>(,)</literal>.

You can think of these missing values as +/-infinity, but they are

special range type values and are considered to be beyond any range

element type's +/-infinity values.

</para>

<para>

This is equivalent to considering that the lower bound is <quote>minus

infinity</quote>, or the upper bound is <quote>plus infinity</quote>,

respectively. But note that these infinite values are never values of

the range's element type, and can never be part of the range. (So there

is no such thing as an inclusive infinite bound &mdash; if you try to

write one, it will automatically be converted to an exclusive bound.)

</para>

<para>

Also, some element types have a notion of <quote>infinity</quote>, but that

is just another value so far as the range type mechanisms are concerned.

For example, in timestamp ranges, <literal>[today,]</literal> means the same

thing as <literal>[today,)</literal>. But <literal>[today,infinity]</literal> means

something different from <literal>[today,infinity)</literal> &mdash; the latter

excludes the special <type>timestamp</type> value <literal>infinity</literal>.

Element types that have the notion of <quote>infinity</quote> can

use them as explicit bound values. For example, with timestamp

ranges, <literal>[today,infinity)</literal> excludes the special

<type>timestamp</type> value <literal>infinity</literal>,

while <literal>[today,infinity]</literal> include it, as does

<literal>[today,)</literal> and <literal>[today,]</literal>.

</para>

<para>