The Relational Taboo - Recursive Dimensions and Topological Ordering (Nested Sets)
The original article was published in the October/November 1992 issue of the Relational Journal, and proposed a way to effectively make ancestor-descendent searches in hierarchies working around relational database limitations, i.e. the lack of recursion capability. Since then variants on the technique appeared at trade journals and books. An excellent explanation is included in the "SQL for Smarties" by J. Celco as well as his more recent "Trees and Hierarchies in SQL fr Smarties". The technique has also been employed in commercial products, such as People Soft's suite and in home-grown database designs.
This is a transcript of the original article circa 1992.