A New Way to Query GISs on the Web

M a y / J u n e 1 9 9 8 I E E E S o f t w a r e 3 1 uery and analysis lie at the heart of a geographic information system.1 The ability to analyze geographical patterns and relationships differentiates GISs from computer cartography, computer-aided design, remote sensing, and database management. Computer scientists have researched relational database query languages for more than a decade, but a spatial query language for GISs has different requirements. As distributed applications proliferate on the Internet and World Wide Web, GISs ranging from corporate information systems to spatially enabled applications have become mainstream. The Web’s heterogeneous environment requires that query mechanisms be both softwareand hardware-neutral. This creates a need for spatial query mechanisms that are distributed and open. The results of a GIS query can contain both geographic and attribute data. This data may be physically separated, possibly residing in different database management systems on different machines. User-selected data can be rendered either as tables (attribute data) or images (geographic data). Query processing for spatial and nonspatial data differ fundamentally. A relational DBMS organizes information in abstract name spaces and lets users refer to the data through their values, while a spatial DBMS organizes information in concrete 2D geometric spaces and lets users designate spatial relationships to retrieve data. A simple example, “Find all farms adjacent to Kruger Park,” illustrates how spatial queries rely on implicit information: “Adjacent” is not a stored attribute or relation but an implicit result of spatial analysis. Serena Coetzee and Judith Bishop, University of Pretoria A New Way to Query GISs on the Web We created a d i s t r ibuted op en spat ia l quer y mechanism that g ives users access to c ross-p lat form, cross-vendor geographic in format ion sys tems v ia the Internet. A Java implementat ion prov ides max imum f lex ib i l i t y fo r Web-based c l ients.