Non-contiguous Sequence Pattern Queries Nikos Mamoulis and Man Lung Yiu   View Paper (PDF)   Return to Session 14: Imprecise Information and Approximate Queries Abstract Non-contiguous subsequence pattern queries search for symbol instances in a long sequence that satisfy some soft temporal constraints. In this paper, we propose a methodology that indexes long sequences, in order to efficiently process such queries. The sequence data are decomposed into tables and queries are evaluated as multiway joins between them. We describe non-blocking join operators and provide query preprocessing and optimization techniques that tighten the join predicates and suggest a good join order plan. As opposed to previous approaches, our method can efficiently handle a broader range of queries and can be easily supported by existing DBMS. Its efficiency is evaluated by experimentation on synthetic and real data. ©2005 Association for Computing Machinery