In the research of xml query language , we consider the requirement of two categories ( for data - centric and for document - centric ) of xml applications and point oat that the basic operations in xml - quey are pattem matching , selection and filtering , and result reconstfuction . the path expression and the flwr expression in xquery are typical structurs tha are comprised of these operations 在对xml查询语言的研究中，从以文档为中心和以数据为中心这两类xml应用需求的分析出发，指出xml查询的基本操作是模式匹配、选择过滤和结果构造， xquery中路径(包括简单路径和正规路径)表达式和flwr表达式是进行这些操作的典型结构。
