1. QBD*: a graphical query language with recursion;Angellacio;IEEE Transaction on Software Engineering,1990
2. Aufaure-Portier, M.A., Trepied, C., 1996. A survey of query languages for geographic information systems. In: Third International Workshop on Interfaces to Databases, Edinbugh, UK, 8–10 July
3. Schema definition and query language for a geographical database system;Barrera;Transactions on Computer Architecture: Pattern Analysis and Image Database Management,1991
4. Car, A., Frank, A., 1994. General principles of hierarchical spatial reasoning – the case of wayfinding. In: Sixth International Symposium on Spatial Data Handling, Edinburgh, Scotland, 5–9 September
5. Christophides, V., Cluet, S., Moerkotte, G. 1996. Evaluating queries with generalized path expressions. In: Proceedings of ACM SIGMOD Conference, Montreal, Canada