Experience with SAND-Tcl: a scripting tool for spatial databases

The use of scripting makes it possible to overcome many important difficulties in the development of database applications. By extending a general-purpose scripting language with constructs derived both from the database kernel and from the intended application domain, issues such as query processing and user interfacing can be approached in an economical and flexible way. This is illustrated by describing our experience with SAND-Tcl, a scripting tool developed by us for building spatial database applications. SAND-Tcl is an extension of the Tcl embedded scripting language with the constructs of the SAND environment for developing applications involving both spatial and non-spatial data. SANDTcl acts as a “glue” to hold together all the subsystems of SAND. In fact, query evaluation plans are SAND-Tcl programs (or scripts) which are written on-the-fly by SAND in response to a query defined by the user. This permits the rapid prototyping of algorithms and makes SAND a useful tool both for applications and research. The focus is on data storage, retrieval operations, and spatial indexing. Implementations of operations such as spatial selection, ranking, and spatial join are given. In addition, tools are described to make possible the construction of graphical user interfaces to a spatial database as well as providing users the ability to view and interact with spatial objects in a graphical manner. This is achieved through the use of SAND-Tcl scripts and the Tk graphical user interface toolkit which is tightly coupled to Tcl.