Querying GML documents: An XQuery based approach

GML is an XML encoding for representation and exchange of geographic information. With the popularity of GML, more and more spatial data exists in GML format. It raises the problem of how to query the data in GML. Since GML is based on XML, query technologies for XML can be employed to GML. However, the fact that GML differs from XML in many aspects makes these technologies not so applicable for GML. The standard query language XQuery, which is recommended by W3C, only applies to GML non-spatial queries. To query GML documents, we propose a GML query processor by extending XQuery in datatypes and spatial operators. The processor can deal with non-spatial and spatial queries, and output the query results in GML format.