7ad2c77a2d
- Removed the reserved alias "base" from the nested set. It's no longer necessary to use that. Use whatever alias you want.
19 lines
1.6 KiB
Plaintext
19 lines
1.6 KiB
Plaintext
Most users at one time or another have dealt with hierarchical data in a SQL database and no doubt learned that the management of hierarchical data is not what a relational database is intended for. The tables of a relational database are not hierarchical (like XML), but are simply a flat list. Hierarchical data has a parent-child relationship that is not naturally represented in a relational database table.
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For our purposes, hierarchical data is a collection of data where each item has a single parent and zero or more children (with the exception of the root item, which has no parent). Hierarchical data can be found in a variety of database applications, including forum and mailing list threads, business organization charts, content management categories, and product categories.
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In a hierarchical data model, data is organized into a tree-like structure. The tree structure allows repeating information using parent/child relationships. For an explanation of the tree data structure, see [http://en.wikipedia.org/wiki/Tree_data_structure here].
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There are three major approaches to managing tree structures in relational databases, these are:
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* the adjacency list model
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* the nested set model (otherwise known as the modified pre-order tree traversal algorithm)
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* materialized path model
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These are explained in more detail in the following chapters, or see
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* [http://www.dbazine.com/oracle/or-articles/tropashko4 http://www.dbazine.com/oracle/or-articles/tropashko4]
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* [http://dev.mysql.com/tech-resources/articles/hierarchical-data.html http://dev.mysql.com/tech-resources/articles/hierarchical-data.html]
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