Publish/subscribe in NonStop SQL: transactional streams in a relational context

Relational queries on continuous streams of data are the subject of many recent database research projects. In 1998 a small group of people started a similar project with the goal to transform our product, NonStop SQL/MX, into an active RDBMS. This project tried to integrate functionality of transactional queuing systems with relational tables and with SQL, using simple extensions to the SQL syntax and guaranteeing clearly defined query and transactional semantics. The result is the first commercially available RDBMS that incorporates streams. All data flowing through the system is contained in relational tables and is protected by ACID transactions. Insert and update operations on any NonStop SQL table can be considered publishing of data and can therefore be transparent to the (legacy) applications performing them. Unlike triggers, the publish operation does not increase the path length of the application and it allows the subscriber to execute in a separate transaction. Subscribers, using an extended SQL syntax, see a continuous stream of data, consisting of all rows originally in the table plus all rows that are inserted or updated thereafter. The system scales by using partitioned tables and therefore partitioned streams.