Query optimization for a distributed geographic information system

Distributed geographic information systems (GISs) have advantages in data s haring, reliability, efficiency and system growth. Query optimization subst antially affects the performance of a distributed GIS. In developing a syst em, query optimization is one of the technical issues that must first be ad dressed. A distributed GIS is different from a non-spatial distributed data base and requires special techniques for query optimization. In this paper, a set of query optimization techniques are presented that we re developed in building a distributed Gls. Two new definitions of spatial operations are introduced that enable us to apply the well-developed operat ion-ordering approach for strategy generation. A Petri net-based straregy-m odeling method is described that is aimed at facilitating strategy generati on and cost estimation. A query optimization algorithm is presented. Cost f unctions and selectivity functions for spatial operations are described as well.