中文摘要：

XML是互联网上数据表示和数据交换的标准。随着大量XML数据的出现,如何有效的查询XML文档内容是值得深入研究的问题。本文阐述了查询XML数据最常用的XPath表达式和XQuery查询语言两种方法,并针对XML查询处理技术和XML查询优化技术进行了详细的探讨,通过对小枝查询的选择度估算问题研究,实现提高XML数据查询性能和执行效率。

英文摘要：

XML is a standard for data representation and data exchange on the internet. With the emergence of a large number of XML data,how to effectively query the content of XML documents becomes an issue worthy of further study. This paper expounds the two most commonly used query languages to query XML data： XPath expression and XQueryquery language. It further explores XML query processing technology and XML query optimization technology. Through the research of twig query selection,we can improve the performance and efficiency of XML query.