GML空间数据查询系统研究

Study on GML Spatial Data Querying System

在网络应用环境下,GIS用户经常需要查询检索不同来源、不同格式的空间数据,完成所需的空间分析功能。但由于GIS软件的封闭性以及空间数据描述标准的缺乏,各厂商的GIS软件只能查询自身格式的空间数据,而无法查询其它GIS的空间数据,导致异构多源空间数据的查询难以实现。GML已经成为空间数据编码、传输;存储、发布的国际标准,为空间数据的描述提供了标准框架,如果所有空间数据都以GML标准来描述或将所有空间数据都转换为GML格式,那么只需要针对GML开发一套功能完善的查询系统,就可以查询检索多源异构空间数据,关键是如何实现这样的GML查询系统。另一方面,随着GML规范的不断完善以及GIS软件厂商对GML规范的广泛支持,大量的GML数据不断涌现,也需要研究GML查询来从大量GML数据中查询检索用户所需数据。本文以XML标准查询语言XQuery为基础,对其进行扩展,增加了通用GML解析、空间数据类型、空间操作算子和R树索引,实现了GML空间数据的本原查询。

In order to fulfill their own spatial analysis functions,GIS users often need to query spatial data in various formats in network application environment. Due to the closeness of GIS software and no standard for spatial data modeling, GIS query functions are usually only applied to the native data format, and would cause the querying to different GISs hardly for implementation. GML has become an international standard for spatial data encoding, transporting, storing and publishing. If all that storing in GML format or all transforming to it, only one GML querying system is needed. On the other hand, as more and more GML data emerging, it also requests GML querying system to meet GIS user[BF]'[BFQ]s needs when querying spatial data from substantive GML system.Currently,querying GML data has been becoming a hot issue in GIS. This paper,based on XQEgine which is an open source software implementing W3X Xquery specifications, extends the standard XML query language Xquery with universal GML parser,spatial data types, spatial operators and spatial index, and thus, one native GML query system is implemented.