"Structure and Value Synopses for XML Data Graphs"

by Neoklis Polyzotis and Minos Garofalakis.
Proceedings of VLDB'2002, Hong Kong, China, August 2002, pp. 466-477.


All existing proposals for querying XML (e.g., XQuery) rely on a pattern-specification language that allows (1) path navigation and branching through the label structure of the XML data graph, and (2) predicates on the values of specific path/branch nodes, in order to reach the desired data elements. Optimizing such queries depends crucially on the existence of concise synopsis structures that enable accurate compile-time selectivity estimates for complex path expressions over graph-structured XML data. In this paper, we extend our earlier work on structural XSketch synopses and we propose an (augmented) XSketch synopsis model that exploits localized stability and value-distribution summaries (e.g., histograms) to accurately capture the complex correlation patterns that can exist between and across path structure and element values in the data graph. We develop a systematic XSketch estimation framework for complex path expressions with value predicates and we propose an efficient heuristic algorithm based on greedy forward selection for building an effective XSketch for a given amount of space (which is, in general, an NP-hard optimization problem). Implementation results with both synthetic and real-life data sets verify the effectiveness of our approach.

[ camera-ready paper (pdf) (ps.gz) | Alkis' talk slides (ppt.gz) ]

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