  Message-oriented-middleware (MOM) has become an small industry. MOM offers
queued transaction processing as an advance over pure client-server transaction
processing. This note makes four points: Queued transaction processing is less
general than direct transaction processing. Queued systems are built on top of
direct systems. You cannot build a direct system atop a queued system. It is
difficult to build direct, conversational, or distributed transactions atop a
queued system. Queues are interesting databases with interesting concurrency
control. It is best to build these mechanisms into a standard database system
so other applications can use these interesting features. Queue systems need
DBMS functionality. Queues need security, configuration, performance
monitoring, recovery, and reorganization utilities. Database systems already
have these features. A full-function MOM system duplicates these database
features. Queue managers are simple TP-monitors managing server pools driven by
queues. Database systems are encompassing many server pool features as they
evolve to TP-lite systems.
