Satisfying Multiple Constraints in Real-Time Database Systems

Real-time database systems, such as military command, control and communication, avionics, radar tracking, and managing automated factories, have timing constraints and temporal consistency constraints. The timing constraint requires a transaction to be completed by a specified deadline. The temporal consistency constraints require that data read by a transaction be up-to-date. In such environments, multiple users share the same database, and some of the users may have restricted access to information from the database. Hence, in addition to maintaining timing and temporal consistency constraints, it is also necessary to provide security for real-time databases. Satisfying more than one constraint in a real-time database system is challenging because maintaining one constraint often means the sacrifice of another. For example, in order to meet a deadline, a transaction may have to read some out-of-date data and as a result, may become temporally inconsistent. Similarly, maintenance of security may require some transactions be blocked or restarted. As a result, those transactions may miss their deadlines. Most research on real-time database systems has addressed timing constraints only and not security or temporal constraints. In this work, we propose to examine multiple constraints in real-time database systems, specifically, maintaining security and temporal consistency in real-time database systems. The objective of this work is twofold. Our first goal is to incorporate security constraints in real-time database systems in such a way that not only is security achieved, but achieving security does not degrade real-time performance significantly. We present new concurrency control algorithms for maintaining security in a real-time database system. These algorithms specially aim at closing or removing covert channels, which facilitate an indirect flow of information between users at two different security levels. We identify the properties of secure real-time database systems. We propose metrics to measure the consequences of introducing a covert channel. We also propose strategies to trade-off between timeliness and security. We present and implement a simulation model for a real-time database system. We implement our new algorithms based these strategies and algorithms and study their performance using a real-time database system simulation.. For our second goal, we propose novel strategies for maintaining temporal consistency. A real-time temporal database system mainly consists of two types of data objects, sensor objects and derived objects. A sensor object is obtained directly from sensors monitoring the real world. The value of a derived object is computed from a set of other objects, known as the read-set …