Yang Xiaochun

An efficient query rewriting approach for Web cached data management

With the internet development, querying data on the Web is an attention problem of involving information from distributed, and often dynamically, related Web sources. Basically, some sub-queries can be effectively cached from previous queries or materialized views in order to achieve a better query performance based on the notion of rewriting queries. In this paper, we propose a novel query-rewriting model, called Hierarchical Query Tree, for representing Web queries. Hierarchical Query Tree is a labeled tree that is suitable for representing the inherent hierarchy feature of data on the Web. Based on Hierarchical Query Tree, we use case-based approach to determine what the query results should be. The definitions of queries and query results are both represented as labeled trees. Thus, we can use the same model for representing cases and the medium query results can also be dynamically updated by the user queries. We show that our case-based method can be used to answer a new query based on the combination of previous queries, including changes of requirements and various information sources.

An Optimized Approach for Extracting Approximate Functional Dependencies in XML Documents

In this paper, the definition of approximate XFDs based on value equality is proposed. Two metrics, support and strength, are presented for measuring the degree of approximate XFD. A basic algorithm is designed for extracting minimal set of approximate XFDs, and then two optimized strategies are proposed to improve the performance. Finally, the experimental results show that the optimized algorithms are correct and effective.

A Filter-Based Uniform Algorithm for Optimizing Top-k Query in Distributed Networks

In this paper we propose a Filter-based Uniform Algorithm (FbUA) for optimizing top-k query in distributed networks, which has been a topic of much recent interest. The basic idea of FbUA is to set a filter at each node to prevent it from sending out the data with little chance to contribute to the top-k result. FbUA can gain exact answers to top-k query through two phrases of round-trip communications between query station and participant nodes. The experiment results show that FbUA reduces network bandwidth consumption dramatically.