Extending SQL for Graphical Display

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Abstract
A language has been designed to describe the cartographic display of query results in geographic information systems. Its syntax is based on SQL, the standard query languages for relational data bases. The syntactical separation of data-base query and display specifications into a query language and graphical presentation language, respectively, is a novel approach. Spatial SQL introduces spatial data types and the corresponding spatial relationships, allowing users to inquire about spatial objects in the familiar SELECT-FROM-WHERE form, extended by spatial conditions. The cartographic display of spatial objects selected is directed with the Spatial SQL-based Graphical Presentation Language (GPL), so that complex graphic descriptions can be formulated in a language similar to SQL. GPL contains commands to direct the display of objects, spatial context, the query window, map scale, etc. This lets users formulate separately queries and display specifications, which are integrated during query processing so that an optimized execution strategy can be achieved in a single step. It overcomes the inherent problem of previous spatial query languages, which concentrated on the retrieval of data from the data base and either tried to integrate the cartographic display into the actual user query or used only default renderings.

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