A DECLARATIVE SPATIAL QUERY PROCESSOR FOR GEOGRAPHIC INFORMATION-SYSTEMS

The design and implementation of a declarative GIS query processor capable of extracting the locations of complex objects from a spatial database is described. The processor extracts such objects from the database in a single, automated step. It also provides extensible support with respect to spatial operators and is independent of the particular spatial and attribute relationships being satisfied. The processor relies on the application of spatial operators that are stored in an extensible database and is guided both by symbolic definitions of the objects being sought and knowledge of the different operators. Search is based upon an efficient query processing algorithm, named forward constraint propagation, that integrates spatial constraint propagation, geometric search using hierarchical data structures, and an effective heuristic used in solving constraint satisfaction problems. Experimental results show that forward constraint propagation is superior to other constraint satisfaction algorithms for large domain sizes and high degrees of constraint.