Models for Hierarchical Data with SQL and PHP by Bill Karwin.
From the description:
Tree-like data relationships are common, but working with trees in SQL usually requires awkward recursive queries. This talk describes alternative solutions in SQL, including:
- Adjacency List
- Path Enumeration
- Nested Sets
- Closure Table
Code examples will show using these designs in PHP, and offer guidelines for choosing one design over another.
May be of interest as a consumer of data stored using one of these designs or even using them more directly.