Web services for accuracy-based spatial query rewriting in a wrapper-mediator system

Web-based federated spatial databases usually do not support accuracy-aware query processing despite growing availability of individual data quality descriptions. This paper introduces a mechanism for making data quality information operational through the process of accuracy-based query rewriting. A number of keywords are added to SQL to express accuracy constraints in a spatial query. Depending on the specification of error in underlying data sets, a query containing accuracy constraints is rewritten as a single or a set of crisp spatial queries, i.e. those that do not require further accuracy-based disambiguation. The rewriting uses binding of GIS spatial operations to error models via a collection of error propagation templates. This mechanism is implemented as a Web service that works in conjunction with a spatial mediator to aid in rewriting spatial queries in the presence of accuracy metadata.