Jinbao Wang

How should we perform anomaly detection on multivariate time-series data with missing data, attribute misplacement and concept drift? The majority of existing anomaly detection methods overlook the fact that data are often of low quality. To address this challenge, we propose an adaptive unsupervised anomaly detection method for low-quality multivariate time series data. Our method introduces a self-attention mechanism that integrates masked information and missing length information to enhance the model's capability in handling incomplete data. Furthermore, we design a deep probabilistic adaptive memory network to improve the model's adaptability to attribute misplacement and concept drift. We also discuss the optimal window size for effectively dealing with concept drift. Comparative experiments on multiple real-world datasets demonstrate that our method can effectively detect anomalies in low-quality multivariate time series data. The experimental results further highlight the robustness of our model, proving its ability to maintain high performance in the presence of data quality issues.

Frequent itemset mining (FIM) and high-utility itemset mining (HUIM) are two important branches of itemset mining which is a key technology of knowledge discovery in many applications. Nowadays, there have been extensive algorithms on FIM and HUIM, but few studies consider frequency and utility together, so skyline frequent-utility itemset mining (SFUIM) is proposed to find useful itemsets with both frequency and utility measurements. Nevertheless, SFUIM is more challenging than FIM and HUIM since the search space is large and the calculation cost is expensive without any threshold, especially on large-scale databases. To address it, this paper proposes a novel prefix-based algorithm PSI* to mine skyline frequent-utility itemsets on massive data. PSI* divides the huge database by prefix-based partitioning, so that the calculation of itemsets with a specific prefix-item only involves a partition instead of the database. A multilevel-index based list is presented to compactly maintain the maximal utility under the frequency constraint, and a novel grid-based structure is devised to organize partitions or items by a designed order. Moreover, four efficient pruning strategies are proposed to prune itemsets as early as possible. Substantial experiments show that the PSI* algorithm has better performance than the state-of-the-art algorithms, obviously on large-scale databases.

Functional dependencies are the most common constraints in the design theory for relational databases, which have very important practical applications in many areas. Different kinds of algorithms are proposed to discover the functional dependencies. However, it is found in this paper that the existing algorithms cannot deal well with massive data which cannot be held entirely in memory due to high memory consumption and high computation cost. In this paper, a novel algorithm FSC is presented to compute functional dependencies on massive data. The two-step execution of FSC relies on a pre-computed update-friendly assistant structure of comparable pairs which reflect the identifier pairs for tuples with at least one equal attribute. In step 1, FSC determines the violated functional dependencies and introduces the selective comparison by comparable pairs to reduce the required pairwise comparison significantly. The direct value-combination compression strategy is devised to process attributes of small cardinality. In step 2, FSC induces the required functional dependencies by the results in step 1. The extensive experimental results, conducted on synthetic and real-life data sets, show that FSC can discover functional dependencies on massive data efficiently.

The data collected in Internet of Thing (IoT) systems (IoT data) have stimulated dramatic extension to the boundary of commercialized data statistic analysis, owing to the pervasive availability of low-cost wireless network access and off-the-shelf mobile devices. In such cases, many data consumers post their queries for urban statistic analysis in the system, like the scales of traffics, and then data contributors in IoT networks upload their contents, which can be evaluated by data brokers and responded to data consumers. However, huge volumes of devices bring large scales of data, constituting heavy burdens for data exchange. Even worse, contents in IoT systems are also sensitive as they are usually linked to private physical status of data contributors. The previous studies for IoT data trading fail to provide comprehensive estimation and pricing towards these difficulties. Therefore, this paper proposes a novel framework for the range counting trading over IoT networks by jointly considering data utility, bandwidth consumption, and privacy preservation. The range counting accumulates the number of data items falling in a concerned range of value, providing important information on the underlying data distribution. This paper first proposes a novel sampling-based method with histogram sketching for range counting estimation. The estimator is proved to be unbiased and achieves advanced performance on variance. Then the framework adopts a perturbation mechanism that can further preserve the results under differential privacy. The theoretical analysis shows that the mechanism can guarantee the privacy preservation under a given size of samples and the accuracy requirement of results. Finally, two types of pricing strategies for range counting trading are introduced for different circumstances, providing holistic consideration on how the parameters given in the estimator should be used for data trading. The framework is evaluated by estimating the air pollution levels and the traffic levels with different ranges on the 2014 CityPulse Smart City datasets. The evaluation results demonstrate that our framework can provide more accurate and reliable statistical information, with reduced bandwidth consumption and strengthened privacy preservation.

Spatial databases store objects with their locations and certain types of attached items. A variety of modern applications have been developed by leveraging the utilization of locations and items in spatial objects, such as searching points of interest, hot topics, or users' attitude in specified spatial regions. In many scenarios, the high and low-frequency items in a spatial region are worth noticing, considering they represent the majority's interest or eccentric users' opinion. However, existing works have yet to identify such items in an interactive manner, despite the significance of the endeavor in decision-making systems. This study recognizes a novel type of analytical query, called top/bottom-k fraction query, to discover such items in spatial databases. To achieve fast query response, we propose a multilayered data summary that is spread out across the main memory and external memory. A memory-based estimation method for top/bottom-k fraction queries is proposed. To maximize the use of the main memory space, we design a data summary tuning method to dynamically allocate memory space among different spatial partitions. The proposed approach is evaluated with real-life datasets and synthetic datasets in terms of estimation accuracy. Evaluation results demonstrate the effectiveness of the proposed data summary and corresponding estimation and tuning algorithms.

Age of Information (AoI) has been proposed to measure the freshness of the sensory data for IoT applications. In Battery-free WSNs (BF-WSNs), The AoI minimization data collection problem has been extensively studied. Apart from data collection, target monitoring is also an important application for BF-WSNs. To capture the freshness of the sensory data, the AoI related to targets (The AoI of targets) needs to be considered. To guarantee the performance of the target monitoring system, the maximum AoI of all targets should be minimized. However, existing works mainly investigated the AoI related to nodes (The AoI of nodes), which is different from the AoI of targets. Also, existing energy models are not practical enough for battery-free nodes. To deal with those problems, in this paper, we first propose a more practical energy model. Then the problem of Maximum AoI minimization for Target monitoring in Battery-free WSNs (MTB) is formally defined based on the proposed energy model. A two-stage algorithm is proposed to solve MTB optimally, in which all nodes in the network are scheduled collaboratively to monitor all the targets in the monitoring field. Extensive simulations and real-world experiments verify the high performance of our algorithm and energy model.