TYPES 

Trees are represented by two types: entree (enumerated tree) and
bitree (bit tree). The corresponding query types are entreequery and
bitreequery.

tree - 
    The tree type represents a node of a tree as a path from the root
    to the node.  A path is generated using each node's number.  Thus,
    the record by '3.4' indicates the 4th child of the 3rd child of
    the root. Numbers at each level begin at 1. For the entree tree
    type, the maximum number of children for each node is 65535. For
    the bitree tree type, the maximum number of children for each node
    is determined during compilation and valid values are 8,16,32
    (default) and 64.  The type is sorted in order of the direct
    traverse of the tree.

treequery - 
    represents a tree node pattern that is used for queries. It's the
    same type as a tree but with the possibility to use some sort of
    regular expression. For example, record '1.2|3' indicates the 2nd
    or 3rd child of the 1st child of the root, and '1.*.4|5' indicates
    the 4th or 5th child of any child of the 1st child of the root.
    The examples given above correspond to all descendant nodes. If
    this is not desirable, it is possible to limit the depth of the
    pattern matching. For instance: '1.2|3.0' and '1.*.4|5.0',
    respectively.

OPERATIONS 

    The following operations are determined for the tree types:
          <,>,<=,>=,= and <>. 
    Also, it's possible to match patterns:
         tree <* treequery 
         treequery >* tree 
    The last two operations return TRUE if the node matches the
    treequery pattern.  Operation 
        tree @> tree 
    returns TRUE if the left argument is the ancestor of the right or
    equal to it.  The respective operation
        tree <@ tree
    returns TRUE if the right argument is the ancestor of the left or
    equal to it (the left argument is the descendant of the right).

FUNCTIONS 

    entree_level(entree) and bitree_level(bitree) return the level of 
    node. 

    entree_next(entree) and bitree_next(bitree) return the next free node. 

    Example of how to add a node:
    select entree_next(tid) from dmoz where tid <* '1.2.3.*.0' order
        by tid desc limit 1;

INDICES 

    Type tree supports two types of indices:
    B-Tree - accelerates operations:
         <,>,<=,>= and =. 
    Supports all features of regular B-tree - unique indices,
    merge-join,...
    GiST - accelerates operations:  
         <,>,<=,>=,=,*>,<*,@> and <@

Arrays of tree

    The following operations are determined for arrays of tree:
        tree[] => tree
        tree   <= tree[]
        tree[]      <* treequery
        treequery   *> tree[]
    The first two operations return true if in the array there is a
    record equal to another operand of the operations. The last 2
    operations return true if there is a record in the array which
    corresponds to the given pattern. These operations can be
    accelerated by constructing GiST-indices.

NOTICES

    1. The following selects are equivalent and return all descendants
    of node 1.1:
    select * from treetbl where treefld >= '1.1' and treefld < '1.2'; 
    select * from treetbl where treefld <* '1.1';
    select id from dmoz where id <@ '1.1';

    2. Insertion into GiST is several times slower than insertion
    into B-Tree, while selection performance is at most 1.5 slower.

EXAMPLES:

    create table dmoz 
    (
        nodename	text, -- the name of node
        nodepath	text, -- path to node
        intid		int,  -- the unique identifier
        id		entree
    );

    To obtain all children of the node: 
    select * from dmoz where id <* '1.2.3.*.0';

    To obtain all decendants of the node: 
    select * from dmoz where id <* '1.2.3' and id != '1.2.3';

    To obtain all children of the node with the calculation of all
    their descendants:
    select *, 
    ( 
        select count(*)-1 from dmoz as d 
        where d.id <* entree2query(dmoz.id)
    ) as descentcount  
    from dmoz where id <* '1.2.3.*.0';