Not all databases are relational. Not all relational databases are built on b-trees. From the summary: > Many people are building queue managers on file syst

Not all databases are relational. Not all relational databases are built on b-trees. From the summary: > Many people are building queue managers on file systems as a transactional resource manager and a TP-lite monitor. An alternative approach is to evolve an Object-Relational database system to support the mechanisms needed to build a queuing system The key word here is evolve. The point is to think of a queuing system in the database as a concept sense, rather than the database as a specific implementation sense.