Traditionally

Geographical Information Systems can only process spatial data in a procedure-oriented way

and the data can' t be treated integrally.This approach greatly limits the development of applications utilizing spatial date.A new and promising method to solve this problem is the spatial structural query language

which extends SQL and provides integrated accessing to spatial data.In this paper

the theory of spatial structural query language is discussed

and a new geographical data model based on the concepts and data model in OGIS is introduced.According to this model

a spatial structural query language—G/SQL is implemented.Through the studies of 9-Intersection Model

G/SQL provided a set of topological relational predicates and spatial functions for GIS application development.The authors have successfully developed a Web-based GIS system—WebGIS—using G/SQL.Experiences show that the spatial operators G/SQL offered are complete and easy-to-use.The BNF representation of G/SQL syntax is included in this paper.