Sketch-based spatial query systems provide an intuitive method of user interaction for<br />spatial databases. These systems must be capable of interpreting user sketches in a way<br />that matches the information that the user intended to provide. One challenge that must be<br />overcome is that humans always simplify the environments they have experienced and this<br />is reflected in the sketches they draw. One such simplification is manifested as aggregation<br />or combination of spatial objects into conceptually or spatially related groups.<br />In this thesis I develop a system that uses reasoning tools of the RCC-8 to evaluate sketchbased<br />queries and provide a method for minimizing the effects of aggregation by<br />determining whether a solution to a query can be expanded if some groups of regions are<br />assumed to be parts of a larger aggregate region. If such a group of regions is found, then<br />this group must be included in the solution. The solution is approximate because the<br />approach taken only verifies that assumed parts of an aggregate are not inconsistent with<br />the configuration of the whole solution. Only cases where the size of the solution equals the<br />size of the query minus one are analysed.<br />It is observed that correctly identifying aggregated regions leads to solutions that are more<br />similar to the original query sketch when the size of every other solution is smaller than the<br />size of the query or when a lower limit is placed on the acceptable size of a solution because<br />the new, expanded or refined solution becomes more complete with respect to the sketch<br />of the query.
