Changes

<p>[[Image:Logical_Graph_Figure_12.jpg|center]]</p>

<p>[[Image:Logical_Graph_Figure_12.jpg|center]]</p>

Back at the abstract level, it takes three nodes to represent the three data records, with a root node connected to two other nodes.  The ordinary bits of data are then treated as labels on the nodes:

Returning to the abstract level, it takes three nodes to represent the three data records illustrated above:  one root node connected to a couple of adjacent nodes.  The items of data that do not point any further up the tree are treated as labels on the record-nodes where they reside, as shown below:

<pre>

<p>[[Image:Logical_Graph_Figure_13.jpg|center]]</p>

          | /                                             

</pre>

Notice that, with rooted trees like these, drawing the arrows is optional, since singling out a unique node as the root induces a unique orientation on all the edges of the tree, with 'up' being the same direction as 'away from the root'.

Notice that drawing the arrows is optional with rooted trees like these, since singling out a unique node as the root induces a unique orientation on all the edges of the tree, with ''up'' being the same direction as ''away from the root''.

==Quick tour of the neighborhood==

==Quick tour of the neighborhood==