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lines 5-53 of file: xrst/table/node_table.xrst
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{xrst_begin node_table}

The Node Table
##############

Discussion
**********
The node table defines a graph that is a tree by specifying
the parent for each node.
The ``node`` table has the following columns:

node_id
*******
This column has type ``integer`` and is the primary key for this table.
Its initial value is zero, and it increments by one for each row.

node_name
*********
This column has type ``text`` and has a different value for every row;
i.e., the names are unique and can act as substitutes for the primary key.
The names are intended to be easier for a human to remember than the ids.

parent
******
This column has type ``integer`` and is the *node_id*
of the parent for this node.
If this node has no parents, *parent* is ``null`` .
Note that this is a value for the primary key in this table, but
the name of this column does not follow the
:ref:`foreign key<database@Foreign Key@parent>` naming convention.

Children
========
The children for node *p* is the sent of *node_id* values
such that the corresponding *parent* is equal to *p* .

Descendant
==========
The set of descendants for a node *p* is the
set children of *p* , grand children of *p* , ... .
{xrst_toc_hidden
    example/table/node_table.py
}
Example
*******
The file :ref:`node_table.py-name`
contains an example ``node`` table.

{xrst_end node_table}