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The entity set expansion problem is to expand a small set of seed entities to a more complete set of similar entities. It can be applied in applications such as web search, item recommendation and query expansion. Traditionally, people solve this problem by exploiting the co-occurrence of entities within web pages, where latent semantic correlation among seed entities cannot be revealed. We propose a novel approach to solve the problem using knowledge graphs, by considering the deficiency (e.g., incompleteness) of knowledge graphs. We design an effective ranking model based on the semantic features of seeds to retrieve the candidate entities. Extensive experiments on public datasets show that the proposed solution significantly outperforms the state-of-the-art techniques.

Modern data analytical tasks often witness very wide tables, from a few hundred columns to a few thousand. While it is commonly agreed that column stores are an appropriate data format for wide tables and analytical workloads, the physical order of columns has not been investigated. Column ordering plays a critical role in I/O performance, because in wide tables accessing the columns in a single horizontal partition may involve multiple disk seeks. An optimal column ordering will incur minimal cumulative disk seek costs for the set of queries applied to the data. In this paper, we aim to find such an optimal column layout to maximize I/O performance. Specifically, we study two problems for column stores on HDFS: column ordering and column duplication. Column ordering seeks an approximately optimal order of columns; column duplication complements column ordering in that some columns may be duplicated multiple times to reduce contention among the queries' diverse requirements on the column order. We consider an actual fine-grained cost model for column accesses and propose algorithms that take a query workload as input and output a column ordering strategy with or without storage redundancy that significantly improves the overall I/O performance. Experimental results over real-life data and production query workloads confirm the effectiveness of the proposed algorithms in diverse settings.

Given a set of client locations, a set of facility locations where each facility has a service capacity, and the assumptions that: (i) a client seeks service from its nearest facility; (ii) a facility provides service to clients in the order of their proximity, we study the problem of selecting all possible locations such that setting up a new facility with a given capacity at these locations will maximize the number of served clients. This problem has wide applications in practice, such as setting up new distribution centers for online sales business and building additional base stations for mobile subscribers. We formulate the problem as location selection query for utility maximization. After applying three pruning rules to a baseline solution,we obtain an efficient algorithm to answer the query. Extensive experiments confirm the efficiency of our proposed algorithm.

Given a multi-features data set, a best preference query (BPQ) computes the maximal preference score (MPS) that the tuples in the data set can achieve with respect to a preference function. BPQs are very useful in applications where users want to efficiently check whether many individual data sets contain tuples that are of interest to them. Although a BPQ can be naively answered by issuing a top-1 query and computing the score from the returned tuple, doing so might require to load a larger number of tuples externally. In this paper, we address the problem of efficient processing BPQs by using lightweight cubic (3-dimensional) views. With these in-memory views, the MPSs of BPQs can be efficiently estimated with an error bound guaranteed, by paying only a small number of I/Os. Extensive experimental results over real-life data sets show that our approximate solution can achieve the efficiency of up to three orders of magnitude compared to exact solutions, with certain accuracy guaranteed.

The problem of monitoring the correlations of discrete streams is to continuously monitor the temporal correlations among massive discrete streams. A temporal correlation of two streams is defined as a tracking behavior, i.e., the most recent pattern of one stream is very similar to a historical pattern of another stream. The challenge is that both the tracking stream and the tracked stream are evolving, which causes the frequent updates of the correlation-ships. The straightforward way of monitoring correlations by brute-force subsequence matching will be very expensive for massive streams. We propose techniques that are able to significantly reduce the number of expensive subsequence matching calls, by continuously pruning and refining the correlated streams. Extensive experiments on the streaming trajectories show the significant performance improvement achieved by the proposed algorithms.

Moving range query over RFID data streams is one of the most important spatio-temporal queries to support valuable information analysis. However, the location uncertainty challenges the query strategy. In this paper, we propose a probability evaluation model in the RFID-enabled monitoring environments and discuss the query optimization techniques under the scenarios of continuous moving range query, which can also be applied into more situations. The extensive experimental evaluation verifies the efficiency and effectiveness of our proposed model and methods.

The tagging technique has been widely applied in existing Web 2.0 systems, where users label resources with tags for effective classification and efficient retrieval of resources. Location-aware geographical tags (geo-tags) are required if users want to mark location-sensitive resources to digital maps. Large volumes of different kinds of user-created tags pose challenges to the effective organization of community resources using tags. Issues such as guaranteeing the quality of tags and supporting various tag-based queries emerge. In this demo, we present MarcoPolo, a Web 2.0 community system that allows users to define the hierarchical textual geo-tags and mark resources to a map using geo-tags. Statistical and feedback mechanisms are applied to guarantee the quality of tags (including geo-tags). The MarcoPolo system provides two effective interfaces for users to browse and search resources: one is the keyword-based interface and the other is the map-based interface.