Real-time event control in active databases

Most existing languages for the specification of active rules are based on the ECA (event-condition-action) paradigm. Usually, rules specified by such languages are triggered by simple events like the update of a tuple in a relational database. We present a specification language that can be used to specify real-time triggering conditions in terms of complex event patterns. Our specification language can be used to formulate complex, triggering conditions for active rules in terms of event patterns that involve sequences, alternations, iterations, and parallel compositions. Also, the language can be used to specify soft, real-time constraints with respect to the minimum/maximum time required/allowed between pairs of events. Our language is designed to be flexible and general in the sense that it can be combined with most ECA rule languages. We formally define the syntax and semantics of the language and we illustrate its use by means of examples. Key Terms: Active rules, Real-time constraints, Event patterns, Event control.