Using the Nested Set Data Model for Breadcrumb Links

Thursday Jul 7th 2005 by Staff

Discover a new way to think about modeling hierarchical data using the nested set model. The more you use this model, the more you come to appreciate the power and inherent simplicity it provides.


It's likely that you have seen what I'm referring to as breadcrumb links before. For example, an online sporting goods store might display breadcrumb links (usually found around the top of the page) so you can see which area of their site you are currently browsing and how you got there:

Home > Sporting Equipment > Tennis > Racquets > Wilson

It's less likely however, that you've heard of what's known as the Nested Set Model of Hierarchies. I know it was new to me when I read about it in a book titled Joe Celko Trees and Hierarchies in SQL for Smarties. So, before I write about how to model breadcrumb link data with this model, I'm going to provide an explanation of what the nested set model is. My explanation might be an oversimplification when compared with the chapter on nested sets from Celko book (and in fact I will be borrowing some ideas and concepts from his book), but it should serve the purpose of getting you familiar with the concept. I would strongly encourage anyone interested in this article to pick up Celko book. (And no, he didn't pay me or ask me give him the ringing endorsement.)

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