QPF A versatile query language for a knowledge-based geographical information system
Jiankang Wu, Тао Чен, Yang Li · International Journal of Geographical Information Systems · 1989
This paper presents a query language, QPF, and describes its implementation in a knowledge-based geographical information system (KGIS). Using QPF, users can retrieve both symbolic and graphical data, and browse through the entire database without prior knowledge of the contents and organization of the KGIS. Processing of complex queries, such as query by object spatial relations, is guided by knowledge represented in frames that simplifies not only query processing, but also query definition and makes querying user-friendly.