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Spatio-temporal data concerning the movement of individuals over space and time contains latent information on the associations among these individuals. Sources of spatio-temporal data include usage logs of mobile and Internet technologies. This article defines a spatio-temporal event by the co-occurrences among individuals that indicate potential associations among them. Each spatio-temporal event is assigned a weight based on the precision and uniqueness of the event. By aggregating the weights of events relating two individuals, we can determine the strength of association between them. We conduct extensive experimentation to investigate both the efficacy of the proposed model as well as the computational complexity of the proposed algorithms. Experimental results on three real-life spatio-temporal datasets cross-validate each other, lending greater confidence on the reliability of our proposed model. Categories and Subject Descriptors: H.3.4 [Information Storage and Retrieval]: Systems and Software--Information networks; E.1 [Data]: Data Structures--Graphs and networks; J.4 [Computer Applications]: Social and Behavioral Sciences General Terms: Algorithms, Experimentation, Verification Additional Key Words and Phrases: Data mining, spatio-temporal databases, social network ACM Reference Format: Lauw, H. W., Lim, E.-P., Pang, H., and Tan, T.-T. 2010. STEvent: Spatio-temporal event model for social network discovery. ACM Trans. Inform. Syst. 28, 3, Article 15 (June 2010), 32 pages. DOI = 10.1145/1777432.1777438 http://doi.acm.org/10.1145/1777432.1777438

While user access control and encryption can protect valuable data from passive observers, these techniques leave visible ciphertexts that are likely to alert an active adversary to the existence of the data. This paper introduces StegFD, a steganographic file driver that securely hides user-selected files in a file system so that, without the corresponding access keys, an attacker would not be able to deduce their existence. Unlike other steganographic schemes proposed previously, our construction satisfies the prerequisites of a practical file system in ensuring the integrity of the files and maintaining efficient space utilization. We also propose two schemes for implementing steganographic B-trees within a StegFD volume. We have completed an implementation on Linux, and results of the experiment confirm that StegFD achieves an order of magnitude improvements in performance and/or space utilization over the existing schemes. Index Terms--Steganography, plausible deniability, security, access control, StegFD, StegBtree.

In recent years, a demand for real-time systems that can manipulate large amounts of shared data has led to the emergence of real-time database systems (RTDBS) as a research area. This paper focuses on the problem of scheduling queries in RTDBSs. We introduce and evaluate a new algorithm called Priority Adaptation Query Resource Scheduling (PAQRS) for handling both single class and multiclass query workloads. The performance objective of the algorithm is to minimize the number of missed deadlines, while at the same time ensuring that any deadline misses are scattered across the different classes according to an administratively-defined miss distribution. This objective is achieved by dynamically adapting the system's admission, memory allocation, and priority assignment policies according to its current resource configuration and workload characteristics. A series of experiments confirms that PAQRS is very effective for real-time query scheduling. Index Terms - Query processing, real-time database systems, memory management, priority scheduling.

Service providers have begun to offer multimedia-on-demand services to residential estates by installing isolated, small-scale multimedia servers at individual estates. Such an arrangement allows the service providers to operate without relying on a high-speed, large-capacity metropolitan area network, which is still not available in many countries. Unfortunately, installing isolated servers could incur very high server costs, as each server requires spare bandwidth to cope with fluctuations in user demand. In this paper, we explore the feasibility of linking up several small multimedia servers to a (limited-capacity) network, and allowing servers with idle retrieval bandwidth to help out servers that are temporarily overloaded; the goal is to minimize the waiting time for service to begin. We identify four characteristics of load sharing in a distributed multimedia system that differentiate it from load balancing in a conventional distributed system. We then introduce a GWQ load sharing algorithm that fits and exploits these characteristics; it puts all servers' pending requests in a global queue, from which a server with idle capacity obtains additional jobs. The performance of the algorithm is captured by an analytical model, which we validate through simulations. Both the analytical and simulation models show that the algorithm vastly reduces wait times at the servers. The analytical model also provides guidelines for capacity planning. Finally, we propose an enhanced GWQ+L algorithm that allows a server to reclaim active local requests that are being serviced remotely. Simulation experiments indicate that the scheduling decisions of GWQ+L are optimal, in the sense that it enables the distributed servers to approximate the performance of a large centralized server. Index Terms--Multimedia-on-demand, distributed servers, load sharing, performance modeling.