Abstract
Selectivity estimation of path expressions in querying XML data plays an important role in query optimization. A path expression may contain multiple branches with predicates, each of which having its impact on the selectivity of the entire query. In this paper, we propose a novel method based on 2-dimensional value histograms to estimate the selectivity of path expressions embedded with predicates. The value histograms capture the correlation between the structures and the values in the XML data. We define a set of operations on the value histograms as well as on the traditional histograms that capture nodes positional distribution. We then construct a cost tree based on such operations. The selectivity of any node (or branch) in a path expression can be estimated by executing the cost tree. Compared with previous methods (which ignore value distribution) our method offers much better estimation accuracy.
This research was partially supported by the grants from 863 High Technology Foundation of China under grant number 2002AA116030, the Natural Science Foundation of China(NSFC) under grant number 60073014, 60273018, the Key Project of Chinese Ministry of Education (No.03044) and the Excellent Young Teachers Program of M0EPRC (EYTP)
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Wang, Y., Wang, H., Meng, X., Wang, S. (2004). Estimating the Selectivity of XML Path Expression with Predicates by Histograms. In: Li, Q., Wang, G., Feng, L. (eds) Advances in Web-Age Information Management. WAIM 2004. Lecture Notes in Computer Science, vol 3129. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-27772-9_41
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DOI: https://doi.org/10.1007/978-3-540-27772-9_41
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