XPQL: a pictorial language for querying geographic data

This paper proposes and discusses an eXtended Pictorial Query Language (XPQL) for geographic data and the possibilities for its use on the Web. This language is mapped on Geographic Markup Language (GML3.0), which is used for transport on to the Web and storage of geographic information, including spatial and non-spatial properties and temporal and topological properties. The XPQL algebra is described and an example of the language given using the implemented prototype. The method used to solve ambiguities arising when drawing the different features of the pictorial query is also explained. Particular attention is given to queries which include temporal constraints and the way to express these.