Query Evaluation in the Object - Oriented GIS

In this paper, we report on experience building our geographic information system GODOT on top of an object-oriented database system. In particular, we describe our experiences and methodology in selecting such a system, some of the problems we encountered, and possible solutions. Speciically, after identifying a range of spatial predicates, we show that the intersection join is of crucial importance for spatial joins. This result together with the concept of the-function (Gaede and G unther 1995) allows us to process queries containing user-deened spatial predicates more eeciently. Next, we show how these results can be combined with spatial access methods (in particular z-ordering) to form an integrated framework for spatial applications. Subsequently, many of the most important algorithms are presented along with a discussion of their merits and failings. We brieey outline how these concepts are integrated into the three-way object-oriented data model of GODOT and present the results of some benchmarks which clearly show the superiority of our concept.