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In a real-time database, correctness of transaction depends not only on the correct implementation, but also depends on the effectiveness of time. Traditional database recovery strategies are adopted to undo all malicious transactions and affected transactions, and then redo the affected transactions. This time-consuming recovery process is not acceptable for real-time databases. Sometimes a transaction may have already exceeded its implementation period, and thus lose the meaning of recovery. By assessing the repair necessity for the affected transaction, a recovery approach is proposed to decide whether to recovery, and then fuse malicious transactions and valuable affected transactions. By this way it can significantly reduce the required number of the transactions needed to undo and redo, avoid worthless recovery operations, and reduce the system I/O and log scanning. So the recovery can be finished in an efficient time.

A scheduling strategy, called Golden Mean (GM), is designed to achieve the dynamic balance between the memory usage minimization and latency minimization by taking the status of the future workload, the current memory consumption and QoS requirement of the query into account. In the GM scheduling strategy, the executing order of the operators is decided uniformly according to the Scoring Function. The static parameters in the Scoring Function can be customized to meet the need of various application scenarios, while the dynamical parameters can be adjusted automatically according to the current system status. In addition, the priority levels of queries can be guaranteed by GM. The experimental results indicate that the GM scheduling strategy is very effective in practice.

Rapid and efficient recovery in the event of site crash is very important for distributed real-time main memory database system. In this paper, the recovery correctness criteria of distributed real-time main memory databases are first given. Then, a time-cognizant dynamic crash recovery scheme (TCDCRS) based on log is presented. TCDCRS uses nonvolatile RAM as logging store and integrates the properties of partitioned logging, ephemeral logging and real-time logging in order to reduce the logging cost as possible during the normal running. During restart recovery after site crashes, a dynamic recovery method based on the classification recovery strategy, which supports concurrent of system services and recovery processing, is adopted to decrease the downtime to the most extent. Experiments and evaluations show that TCDCRS has better performances than traditional recovery schemes in two aspects: the missing deadlines ratio of transactions and the time of system denying services after crashes.

This paper discusses the order-based deadlock prevention protocol with parallel requests (ODP3) [1]. From the analysis of theorems about ODP3, we found that the conclusions of paper [1] are not correct. The ODP3 method is not free from deadlock and live-lock. An example is given to illustrate our deduction.

Recovery processing in embedded real-time databases (ERTDBs) is more complex than traditional databases. In this paper, the classifications and consistency constraints of data and transactions in embedded real-time databases are given first. Then time-cognizant recovery principles for different classes of data and transactions are discussed. In terms of these principles, a time-cognizant recovery scheme based on real-time logging is presented, which is suitable for a class of embedded real-time databases applications. Performance evaluations show that the suggested scheme has better performances than traditional recovery techniques in two aspects: the missing deadlines percent of transactions and the time of system denying services after crashes.

Data management issues in mobile computing environments have got lots of concerns of relevant researchers. Among these research topics, data broadcast has been extensively investigated due to its advantages such as scalability and bandwidth effectiveness. While plenty of works have been done on this subject, it is still less touched when data broadcast is used to deliver constantly updated real-time data to read-only transactions with deadlines. In this paper, we first deeply analyze the data dissemination requirements for read-only transaction processing in mobile real-time computing environments and formally define several performance objectives. Then a novel updates dissemination protocol called mixed real-time data broadcast is proposed. In mixed real-time data broadcast, a set of new techniques including reducing the length of consistency intervals, immediate updates dissemination policy and on-demand data delivery are incorporated seamlessly. Moreover, an enhanced index structure is designed for read-only transactions to judge precisely when to request the desired data. Simulation results show that the proposed protocol can provide higher data currency and lower miss rate compared with existing updates dissemination protocols and is more appropriate for mobile real-time computing environments.

Mobile distributed real-time databases are needed in security-critical applications, e.g., e-commerce, stock trading system, and military applications. In these applications, mobile distributed real-time database systems have to simultaneously satisfy two requirements in guaranteeing data security and minimizing the deadline miss ratio for admitted transactions. Multilevel secure database system based on mandatory access control can prevent direct unlawful information flows between transactions belonging to different clearance levels. However, it cannot prevent the covert communications between transactions belonging to different clearance levels. This paper presents a secure hybrid optimistic real-time concurrency control protocol (SHORTCC). The protocol not only considers carefully the inherent characteristics of mobile environment and the timing constraints of time-critical applications, but also achieves data security without sacrificing real-time performance significantly.

The grid technology and distributed simulation functionality were firstly introduced. We proposed two approaches to integrate actual distributed simulation application into grid environment. The first one is to take advantage of grid technology to support distributed simulation, which is independent of the development of distributed simulation. The second one consists of using specific extensions of distributed simulation based on grid technology. We mainly focused on the latter and argued about integrating HLA technology into OGSA model in detail. Under the above discussion, we defined G-RTI concept, which means the Runtime Infrastructure (RTI) based on grid technology.

Aimed at coordinated resource sharing in distributed, heterogeneous dynamic environment, OGSA supports distributed simulation effectively in resource management. GT3 Core provides a structure of service container, based on which a new mode of distributed simulation system has been designed. The new mode realized the separation of simulation resource and simulation applications, and supplied a simulation server responsible for the organization of simulation resource. The server provides service index for higher simulation applications and enable the interaction among them. Under this new simulation mode, a combat simulation application has been developed as a prototype. It achieved well reusability, portability of simulation resource, and supported heterogeneous, cross-platform application development.

The common feature of the XML query languages is the use of path expressions to query XML data. To speed up the processing of path expression queries, it is important to be able to quickly determine ancestor-descendant relationship between any pair of nodes in the hierarchy of XML data. At the same time, keyword search is also important to query XML data with a regular structure, if the user does not know the structure or only knows the structure partially. In this paper, we propose a new approach about storing and querying XML data in the RDBMS basing on the idea of the numbering schema and the inverted list. Our approach allows us to quickly determine ancestor-descendant relationship between any pair of nodes in the hierarchy of XML data, which is particularly, highly effective for the searching paths that are very long or unknown. Examples have demonstrated that our approach can effectively supports both query powers in XQuery and keyword searches. Our approach is flexible enough to support XML documents both with schema and without schema, and applications both retrieval and update.