XPath query optimization method and system

Abstract

The invention discloses an XPath query optimization method and system. The method comprises the following steps of: counting structural summary information of an extensive makeup language (XML) document through hierarchical encoding; counting value summary information by using a value-coding histogram and RPST, and performing an optimization algorithm for query optimization on an XPath expression by utilizing the statistical information, wherein the query optimization algorithm comprises the following steps of: 101-102, initializing a data structure and processing a single-step path; 103, judging whether a non-estimated path exists; 104, judging the path type; 105-109, estimating connection with lowest cost in all possible connection of a long path, and updating a cost matrix and a result set matrix by using corresponding data; 110-114, estimating an arrangement sequence with lowest path in a predicate path, updating a cost matrix and a result set matrix by using the corresponding data, and resorting the predicates according to an optimized sequence; and 115, reconstructing a query plan. According to the XPath query optimization method and system, the XPath query sentences can be effectively optimized, and the execution efficiency of the XPath query sentences is greatly improved.

Description

technical field [0001] The invention relates to the technical field of databases, in particular to an XPath query optimization method and system. Background technique [0002] In recent years, more and more data are described by XML and transmitted and exchanged on the network. The rapid expansion of XML data has brought new problems to the field of computer science: how to effectively store and quickly retrieve XML data. To store and query massive XML data on the Internet in the form of a database is a mainstream idea about XML data processing at present. Query processing is one of the essential and most important functions of any database system. As an important part of query processing, query optimization technology is often the key factor affecting query efficiency. Due to the complexity of the XML data model and its increasing scale, as well as the complexity of the XML query itself, the performance of the XML query is often not ideal. People have used quite mature q...

AI Technical Summary

Problems solved by technology

The irregularity of XML data is an important challenge to traditional statistical information methods. Its data distribution makes some traditional distribution assumptions difficult to establish, and the complexity of the structure brings storage and calculation difficulties to obtain relatively accurate statistical information. , the orderliness of XML data also restricts the flexibility of conversion rules

All these problems make it impractical to use the traditional cost estimation method in xml, which will bring large errors

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