Re: How to represent a tree-structure in a relational database

Stuart,

> I don't think I'd be comfortable with having the node_level column in the
> table structure. First, because you can derive that value using a function,
> it's duplicate data. Second, if you decide to take an entire segment of your
> hierarchy and move it under another node (by changing the value of
> node_linkup/ParentCategoryID), you'll need to recalculate all of those
> node_level values. And all the node_level values underneath it.

I can see that. I suppose it depends on the data you're storing. The
project I was working on tracked grocery inventory for a delivery
service, and thus each item had a fixed "level" in the heirarcy (Food
Class, Food Type, Manufacturer, and Item) and thus while items might get
reassigned *across* the heirarcy, they did not get re-assigned *up and
down* the heirarcy.

Also, I can't think of a way to represent the tree in pure SQL without
having the level identifiers (and a fixed number of levels).

> We've done a similar thing for Java. It was ridiculously easy to create a
> TreeModel wrapped around this data. Almost too easy; it made me feel dirty.

Great. Maybe I'll buy it from you if I ever need to use Java :-)

-Josh

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