<row><entry><literal>&amp;&amp; (polygon,polygon)</literal></entry></row>
     <row><entry><literal>&lt;&lt;| (polygon,polygon)</literal></entry></row>
     <row><entry><literal>&amp;&lt;| (polygon,polygon)</literal></entry></row>
     <row><entry><literal>|&gt;&gt; (polygon,polygon)</literal></entry></row>
     <row><entry><literal>|&amp;&gt; (polygon,polygon)</literal></entry></row>

     <row>
      <entry valign="middle" morerows="5"><literal>quad_point_ops</literal></entry>
      <entry><literal>|&gt;&gt; (point,point)</literal></entry>
      <entry valign="middle" morerows="5"><literal>&lt;-&gt; (point,point)</literal></entry>
     </row>
     <row><entry><literal>&lt;&lt; (point,point)</literal></entry></row>
     <row><entry><literal>&gt;&gt; (point,point)</literal></entry></row>
     <row><entry><literal>&lt;&lt;| (point,point)</literal></entry></row>
     <row><entry><literal>~= (point,point)</literal></entry></row>
     <row><entry><literal>&lt;@ (point,box)</literal></entry></row>

     <row>
      <entry valign="middle" morerows="9"><literal>range_ops</literal></entry>
      <entry><literal>= (anyrange,anyrange)</literal></entry>
      <entry valign="middle" morerows="9"></entry>
     </row>
     <row><entry><literal>&amp;&amp; (anyrange,anyrange)</literal></entry></row>
     <row><entry><literal>@&gt; (anyrange,anyelement)</literal></entry></row>
     <row><entry><literal>@&gt; (anyrange,anyrange)</literal></entry></row>
     <row><entry><literal>&lt;@ (anyrange,anyrange)</literal></entry></row>
     <row><entry><literal>&lt;&lt; (anyrange,anyrange)</literal></entry></row>
     <row><entry><literal>&gt;&gt; (anyrange,anyrange)</literal></entry></row>
     <row><entry><literal>&amp;&lt; (anyrange,anyrange)</literal></entry></row>
     <row><entry><literal>&amp;&gt; (anyrange,anyrange)</literal></entry></row>
     <row><entry><literal>-|- (anyrange,anyrange)</literal></entry></row>

     <row>
      <entry valign="middle" morerows="9"><literal>text_ops</literal></entry>
      <entry><literal>= (text,text)</literal></entry>
      <entry valign="middle" morerows="9"></entry>
     </row>
     <row><entry><literal>&lt; (text,text)</literal></entry></row>
     <row><entry><literal>&lt;= (text,text)</literal></entry></row>
     <row><entry><literal>&gt; (text,text)</literal></entry></row>
     <row><entry><literal>&gt;= (text,text)</literal></entry></row>
     <row><entry><literal>~&lt;~ (text,text)</literal></entry></row>
     <row><entry><literal>~&lt;=~ (text,text)</literal></entry></row>
     <row><entry><literal>~&gt;=~ (text,text)</literal></entry></row>
     <row><entry><literal>~&gt;~ (text,text)</literal></entry></row>
     <row><entry><literal>^@ (text,text)</literal></entry></row>
    </tbody>
   </tgroup>
  </table>

 <para>
  Of the two operator classes for type <type>point</type>,
  <literal>quad_point_ops</literal> is the default.  <literal>kd_point_ops</literal>
  supports the same operators but uses a different index data structure that
  may offer better performance in some applications.
 </para>
 <para>
  The <literal>quad_point_ops</literal>, <literal>kd_point_ops</literal> and
  <literal>poly_ops</literal> operator classes support the <literal>&lt;-&gt;</literal>
  ordering operator, which enables the k-nearest neighbor (<literal>k-NN</literal>)
  search over indexed point or polygon data sets.
 </para>

</sect2>

<sect2 id="spgist-extensibility">
 <title>Extensibility</title>

 <para>
  <acronym>SP-GiST</acronym> offers an interface with a high level of
  abstraction, requiring the access method developer to implement only
  methods specific to a given data type. The <acronym>SP-GiST</acronym> core
  is responsible for efficient disk mapping and searching the tree structure.
  It also takes care of concurrency and logging considerations.
 </para>

 <para>
  Leaf tuples of an <acronym>SP-GiST</acronym> tree usually contain values
  of the same data type as the indexed column, although it is also possible