PQL*: An Extended Pictorial Query Language for Querying Geographical Databases using Positional and OLAP operators

The authors propose a declarative Pictorial Query Language (PQL*) able to expresses queries on an Object-Oriented Geographic database (GDB) drawing the features which form the query. These features refer to the classic ones of a GDB (geopoints, geo-polyline, and geo-region) and define the alphabet of the above mentioned language. This language uses, in addition to the classic operators (topologic and metric), also the positional operators with a set of relative specification. These specifications, for example, concerning the at_North_of operator, are: Completely at_North_of, Only at_North_of, Partially at_North_of, and Also at_North_of. Also the possibility to use multidimensional data, stored in a Multidimensional Database (MDDB), is discussed. The links between the two environments by means of geographic dimension that can be present in a data cube using OLAP operators are defined.