基于XQuery的GML查询语言研究

随着GML规范的不断完善及GIS软件厂商的广泛支持,越来越多的空间数据以GML格式存储,GML空间数据的查询已成为GIS研究的热点问题。传统的关系数据库查询语言SQL是针对平面的二维关系数据而设计的,并不适合XML/GML半结构化数据的查询;商品化GIS软件的查询系统只能查询自身的空间数据而无法查询其它GIS系统的空间数据;XML查询的研究为GML查询奠定了一定的基础。首先针对GML查询存在的问题,提出了扩展XQuery是GML查询语言实现的最佳选择;结合XML查询语言和空间数据查询语言,提出了GML查询语言的特征和GML查询语言系统框架;并根据GML空间数据的特点,以XML标准查询语言XQuery为基础,提出了XQuery空间扩展的内容;开发了GML空间数据查询语言GMLXQL,实现了GML空间数据的本原查询。

Xquery based GML query language

With the development of GML specification and its broad supporting by many GIS software vendors, more and more spatial data has been stored in GML format. Querying GML spatial data has been becoming the hot issue in GIS. Traditional relational database query language SQL is designed for relational tables, and not suitable for XML or GML semistructured data; The query systems of commercial GIS software are usually only applicable to the native data formats. The study on XML query establishes the basis for GML query. To the existing issues of GML query, extending XQuery is the best method to develop GML query language.Integrating the characteristics of XML query language and of spatial query language, the characteristics of GML query language and the architecture framework of GML querying system are proposed. Taking the characteristics of GML data into account, the contents of spatial extension to XQuery are suggested. Consequently one GML query language GMLXQL based on XQuery is developed,and native query over GML data is realized.