GXQuery: A GML spatial data query language

GML spatial data query language is a very important part of native GML spatial database system, it is an indispensable component to GML documents for spatial data query as well. As the data model has significant difference between XML/GML and relational database, it's not suitable using SQL or extending SQL to query GML spatial data. XQuery is W3C recommendation for XML data query, directly using XQuery to query GML spatial data, only the GML non-spatial data can be queried, the GML spatial data can not be queried because of GML's spatial characteristics. Integrally referring previous research achievements, this paper further studied GML spatial data query language based on XQuery and name it GXQuery in order to reflect the integration of GML and XQuery, problem of GML spatial data query, reasons for extending XQuery to support GML spatial data query, features of GML spatial data query language, content of XQuery spatial extension, architecture of GXQuery, implementation methods of GXQuery were detially studied and discussed, and typical query examples of GXQuery were also given.