Equivalence of views by query capacity

摘要

The ability of view users to retrieve information contained in a database is studied. A measure of this ability, called “query capacity,” is introduced and shown to be valuable for defining important concepts concerning views. Three such notions, namely equivalence, redundancy, and decomposition of views, are identified and investigated. A key tool, called “template substitution,” is introduced to aid in these investigations. Among the major results obtained are the following: (1) Characterizations of view equivalence and redundancy in views. (2) The decidability of view equivalence. (3) A technique to eliminate redundancy in views. (4) The decomposition of a view into an essentially unique normal form.