Numerous federal agencies produce official statistics made accessible to ordinary citizens for searching and data retrieval. This is frequently done via the Internet through a Web browser interface. If this data is presented in textual formatT T he SAND Spatial Browser is part of the SAND System whose server side contains a spatial database system that facilitates organization (that is, indexing) of spatial and nonspatial data [1] to support efficient query processing. This database system handles any two or higher dimensional data with extent (for example, country boundaries, river paths), as well as point data (for example, city locations). It facilitates the response to queries involving this data such as finding the closest hazardous waste site to the border of a particular state.Users access and manipulate spatial and nonspatial data using the SAND Spatial Browser in a manner similar to that used in spreadsheets where the map plays the same as a relation in a relational database management system. In particular, operations can be specified as compositions of maps with the output of one or more operations serving as input to other operations that can be saved for use as input to
The rationale behind the design of a JAVA TM spatial index applet is described that enables users on the worldwide web to experiment with different variants of the R-tree. The applet is part of the VASCO system that contains JAVA TM applets for a large set of hierarchical spatial data structures. The R-trees can be built using different splitting rules and include the R* -tree. The applet enables users to see in an animated manner how a number of basic spatial database search operations are executed for them. The spatial operations are spatial selection (i.e., a window or spatial range query) and a nearest neighbor query that enables ranking spatial objects in the order of their distance from a given query object. The results of the different splitting rules and the algorithms are visualized and animated in a consistent manner using the same primitives and colors so that the differences between the effects of the rules can be easily understood. The applet can be used to monitor the performance of spatial databases that use an R-tree spatial index as well as tune them by observing their behavior for different distributions of data. The applet can be found at
Features of the VASCO R-tree JAVA TM applet are described to support its demonstration. This includes an explanation of the different R-tree node splitting methods that are implemented in VASCO and of the functionality of the control panel of the applet. The applet enables users to visualize the different variants of the R-tree as well as observe their behavior for finding the nearest neighbors to a query point and the objects within a given query window in an incremental manner. The applet can be found at http://www. cs. umd. edurhjs/rtrees/index .html.
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