Generalization and a framework for query modification

The rigidity and limited expressiveness of relational queries often require that a query be iteratively modified. An initial query is posed, and once it is discovered that the answer does not meet the additional constraints, which are not expressed in the relational query, it is necessary to modify the query in a way such that those constraints are satisfied. The aim of this work is to capture this iterative process by extending the query model. Extended queries, which express additional constraints on the answer set and designate some of the conditions in the relational query as flexible, are defined. The query modification operators modify flexible constraints to satisfy an extended query. The query modification operation, generalization, is described. The conditions under which generalization is applicable are identified. Rules of generalization are proposed, and an algorithm for picking a minimal generalization is suggested