中文摘要：

真值发现作为整合由不同数据源提供的冲突信息的一种手段,在传统数据库领域已经得到了广泛的研究.然而现有的很多真值发现方法不适用于数据流应用,主要原因是它们都包含迭代的过程.针对一种特殊的数据流——感知数据流上的连续真值发现问题进行了研究.结合感知数据本身及其应用特点,提出一种变频评估数据源可信度的策略,减少了迭代过程的执行,提高了每一时刻多源感知数据流真值发现的效率.首先定义并研究了当感知数据流真值发现的相对误差和累积误差较小时,相邻时刻数据源的可信度变化需要满足的条件,进而给出了一种概率模型,以预测数据源的可信度满足该条件的概率.之后,通过整合上述结论,实现在预测的累积误差以一定概率不超过给定阈值的前提下,最大化数据源可信度的评估周期以提高效率,并将该问题转化为一个最优化问题.在此基础上,提出了一种变频评估数据源可信度的算法——CTF-Stream（continuous truth finding over sensor data streams）,CTF-Stream结合历史数据动态地确定数据源可信度的评估时刻,在保证真值发现结果达到用户给定精度的同时提高了效率.最后,通过在真实的感知数据集合上进行实验,进一步验证了算法在处理感知数据流的真值发现问题时的效率和准确率.

英文摘要：

As a method of assessing validity of conflicting information provided by various data sources, truth discovery has been widely researched in the conventional database community. However, most of the existing solutions of truth discovery are not suitable for applications involving data streams, mainly because their methods include iterative processes. This paper studies the problem of continuous truth discovery in a special kind of data streams-sensor data streams. Combining with the characteristics of sensor data itself and its application, a strategy is proposed based on changing the frequency of assessing source reliability to reduce the iterative processes, and therefore to improve the efficiency of truth discovery in multiple-source sensor data streams. First, definitions are provided on when the relative errors and accumulative errors are relatively small, and the necessary conditions of the variation on source reliability from adjacent time points. Next, a probabilistic model is given to predict the probability of meeting these necessary conditions. Then, by integrating the above conclusions, maximal assessing period of source reliability is achieved, under the condition that the cumulative error of prediction is smaller than the given threshold in a certain confidence level of probabilities, in order to improve efficiency. Thus the truth discovery problem is transformed into an optimization problem. Furthermore, an algorithm, CTF-Stream（continuous truth finding over sensor data streams） is constructed to assessing source reliability with changeable frequencies. CTF-Stream utilizes the historic data to dynamically determine the time needed to assess the source reliability, and finds the truth with a certain accuracy given by customers while improving the efficiency. Finally, both efficiency and accuracy of the presented methods for truth discovery in sensor data streams are validated by conducting the extensive experiments on real sensor dataset.