Database systems for real-time applications must satisfy timing constraints associated with transactions. Typically, a timing constraint is expressed in the form of a deadline and is represented as a priority to be used by schedulers. Recently, security has become another important issue in many real-time applications. In many systems, sensitive information is shared by multiple users with different levels of security clearance. As more advanced database systems are being used in applications that need to support timeliness while managing sensitive information, there is an urgent need to develop protocols for concurrency control in transaction management that satisfy both timing and security requirements. In this paper, we propose a new multiversion concurrency control protocol that ensures that both security and real-time requirements are met. The proposed protocol is primarily based on locking.

Most of the proposed concurrency control protocols for real-time database systems (RTDBS) are based on serializability theorem. Owing to the unique characteristics of real-time database applications and the importance of satisfying the timing constraint of the transactions, serializable concurrency control protocols are not suitable for RTDBS for most cases. In this paper, another notion of correctness, similarity, is used for concurrency control in a RTDBS, for instance, a stock trading database system. Similarity is a less restrictive notion comparing with serializability. By studying the correctness requirements of the stock trading database applications, a real-time two phase locking protocol, High Priority 2 Phase Locking (H2PL) is re-defined based on similarity. Although the new protocol cannot ensure serializability, the concurrency of the system is higher and the amount of inconsistency in the database is tolerable. On the other hand, the performance of the whole system can be much improved. Keywords : real-time database systems, applications, concurrency control, Similarity 2 1

Concurrency control protocols based on multiversions have been used in some commercial transaction processing systems in order to provide the serializable executions of transactions. In the existing protocols, transactions are allowed to read only the most recent version of each data item in order to ensure the correct execution of transactions. However, this feature is not desirable in some advanced database systems which have more requirements such as timing or security constraints besides serializability. In this paper, we propose a new correctness criteria, called F-serializability, for multiversion concurrency control protocols. It is the extended definition of `1-serial' and relaxes the condition so that a protocol provides not only the most recent version but also the previous one to transactions, if necessary. We prove that whenever a multiversion schedule is F-serializable, the schedule is also one-copy serializable. This is the first contribution of our paper. Next, we propos...

ACTIVE DATABASE MANAGEMENT SYSTEMS can provide general solutions to data management problems in control applications. This thesis describes how traditional control algorithms and high-level operations in a control system can be combined by using an embedded active object-relational database management system as middleware. The embedded database stores information about the controlled environment and machinery. The control algorithms execute on a separate real-time server. Active rules in the database are used to interface the model of the environment, as stored in the database, and the control algorithms. To improve information access, the control system is tightly integrated with the database query processor. A control-application language specifies high-level manufacturing operations which are compiled into queries and active rules in the database. The thesis describes how the generated active rules can be organized to solve problems with rule interaction, rule cycles, and cascading ...

I hereby declare that I am the sole author of this thesis. I authorize the University of Waterloo to lend thesis to other institutions or individuals for the purpose of scholarly research. B.R. Pekilis I further authorize the University of Waterloo to reproduce this thesis by photocopying or by any other means, in total or in part, at the request of others institution or individuals for the pur-pose of scholarly research. B.R. Pekilis ii The University of Waterloo requires the signatures of all persons using or photocopying this thesis. Please sign below, and give address and date. iii The focus of the research presented in this thesis is on session-oriented, soft real-time systems whose behavior is specified using the ITU Specification and Description Language

Meeting hard deadlines while also ensuring the integrity of shared data is a difficult problem in real-time systems design. We discuss the key differences between database concurrency control and concurrency control for hard-real-time systems and describe an approach to adapting advanced concurrency control techniques to systems requiring analytic worst-case latency guarantees. We describe an example concurrency control technique, implementable with simple and low-overhead algorithms and data structures, which completely avoids interference between queries and updaters. This report offers a high-level overview and introduction to the problem and approach. Details are provided in other reports [SY92a, SY92b]. Introduction Tasks in hard-real-time systems (HRTS) often cooperate by accessing shared data. The problems of HRTS scheduling involve not only guaranteeing schedulability but also ensuring that shared data will not be corrupted. Ensuring shared data consistency has been extensivel...