I'm passing along an article I saw at DevX.
-David
"Represent hierarchical data structures in a relational database."
http://www.vbpj.com/upload/free/features/vbpj/2001/07jul01/sqlpro0107/rein01
07/rein-1.asp
Here are the first few paragraphs:
"A tree data structure, like a corporate organization chart, shows the
relationships between various pieces of information. How you use the data
determines the method you use for storing it. I'll demonstrate a number of
techniques and show you how to use them in different situations."
"You can represent trees in a relational database in one of three ways: with
the one-to-one parent-child method, the one-to-many parent-child method, or
what Joe Celko calls the nest set method (see Resources). First, with the
one-to-one method, you can store the data for each node in a single database
table. You save the information about the relationships between nodes in the
same table as the information contained in the node. Second, with the one-to
-many method, you use two tables: one with the node information and a second
with the relationship information. When you need to store an exact
representation of the entire tree, you can use a third method, the nest set
method, which also involves two tables. The first table contains the node
information, and the second identifies each node and references the node
information table. The second table doesn't define any relationships-the
relationships are derived from the identifiers of each node."
"I'll use a corporate organization chart to demonstrate each technique. An org
chart represents a company's chain of command
graphically. A typical chart shows the president or CEO at the top and the
field workers at the bottom."
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