If I remember correctly (the book is on my desk at work) he says that adjacency-list hierarchies, without the support of certain DB-specific functionality, can be an antipattern.<p>For example, if you&#x27;re using a database without window functions, obtaining the entire tree in one query is impossible. Also, deleting nodes without removing the subtree is complicated compared to other approaches like Path Enumeration, Nested Sets and Closure Tables.<p>In the application I&#x27;m currently writing (with PostgreSQL 9.5) I opted to use the adjacency list approach, mainly due to its simplicity; nothing other than the parent_id field has to be maintained.