Updates and view maintenance in soft real-time database systems

Abstract

A database system contains base data items which record and model a physical, real world environment. For better decision support, base data items are summarized and correlated to derive views. These base data and views are accessed by application transactions to generate the ultimate actions taken by the system. As the environment changes, updates are applied to the base data, which subsequently trigger view recomputations. There are thus three types of activities: base data update, view recomputation, and transaction execution. In a real-time system, two timing constraints need to be enforced. We require transactions meet their deadlines (transaction timeliness) and read fresh data (data timeliness). In this paper we define the concept of absolute and relative temporal consistency from the perspective of transactions. We address the important issue of transaction scheduling among the three types of activities such that the two timing requirements can be met. We also discuss how a real-time database system should be designed to enforce different levels of temporal consistency.