XPath for Querying GML-Based Representation of Urban Maps

Geography Markup Language (GML) has been established as the standard language for the transport, storage and modelling of geographic information. In this paper we study how to adapt the XPath query language to GML documents. With this aim, we have defined a XPath based query language which handles the “semantic structure” of GML. Our approach focuses on querying urban maps whose representation is based on GML. We have developed a system called UALGIS, in order to implement the approach. Such system stores GML documents by means of the PostGIS RDBMS. In order to execute semantic-based XPath queries we have defined a translation of the queries into SQL. Such translation takes into account the GML schema. Finally, the system allows to visualize the result. With this aim, the result of a query is exported to the Keyhole Markup Language (KML) format.