An XPath Algebraic Characterization of A ( k ) and P ( k ) Indices with Applications to Query Processing

Recent studies have proposed structural summary techniques for path query evaluation on semi-structured data sources. One major line of this research has been the introduction of the DataGuide, 1-index, 2-index, and A(k) indices, and subsequent investigations and generalizations. Another recent study has considered structural characterizations of fragments of XPath, the standard path navigation language for XML documents. In this paper we provide a new perspective on XPath query processing which brings together these two areas of research on structural indices and query languages. In particular, we give a precise characterization of the A(k) and P(k) indices in terms of certain algebraic fragments of XPath. With an eye towards applying this result to XPath query processing, we (1) show how expressions in these fragments can be evaluated directly on the corresponding indices; (2) develop a labeling scheme for A(k) and P(k) partition blocks, using algebraic expressions; and (3) leverage these results to develop general techniques for making effective use of A(k) and P(k) indices for important practical classes of XPath.