Along with single word query, phrase query is frequently used in digital library. This paper proposes a new partition based hierarchical index structure for efficient phrase query and a parallel algorithm based on the index structure. In this scheme, a document is divided into several elements. The elements are distributed on several processors. In each processor, a hierarchical inverted index is built, by which single word and phrase queries can be answered efficiently. This index structure and the partition make the postings lists shorter. At the same time, integer compression technique is used more efficiently. Experiments and analysis show that query evaluation time is significantly reduced.
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