Where Do Time Constraints Come From? Where Do They Go?

While a lot of work has been done in real-time systems, in real-time database systems, and more recently, in real-time active databases on the topic of time constrained processing of tasks and transactions, very little work exists that deals with the origin of the time constraints associated with the data, the events, and the actions. In this paper we identify the sources and semantics of time constraints and show that it is important to minimize the number of “mandated†timing requirements and also weaken the implications of timing constraint violations. The Event-Condition-Action rules of active real-time databases provide a useful framework to specify the timing properties of interest as well as the actions to be taken when the properties are violated. That is, an active real-time database can be made to store the data pertaining to the controlled system as well as the meta-data about the controlling system.