Fast Matching of Twig Patterns

Twig pattern matching plays a crucial role in xml data processing. Existing twig pattern matching algorithms can be classified into two-phase algorithms and one-phase algorithms. While the two-phase algorithms (e.g., TwigStack) suffer from expensive merging cost, the onephase algorithms (e.g., TwigList, Twig2Stack, HolisticTwigStack) either lack efficient filtering of useless elements, or use over-complicated data structures. In this paper, we present two novel one-phase holistic twig matching algorithms, TwigMix and TwigFast, which combine the efficient selection of useful elements (introduced in TwigStack) with the simple lists for storing final solutions (introduced in TwigList). TwigMix simply introduces the element selection function of TwigStack into TwigList to avoid manipulation of useless elements in the stack and lists. TwigFast further improves this by introducing some pointers in the lists to completely avoid the use of stacks. Our experiments show TwigMix significantly and consistently outperforms TwigList and HolisticTwigStack (up to several times faster), and TwigFast is up to two times faster than TwigMix.