A More Aggressive Use Of Views To Extract Information
Nam Huyn · 1996
Much recent work has focussed on using views to evaluate queries. More specifically, queries are rewritten to refer to views instead of the base relations over which the queries were originally written. The motivation is that the views represent the only ways in which some information source may be accessed. Another use of views that has been overlooked becomes important especially when no equivalent rewriting of a query in terms of views is possible: even though we cannot use the views to get all the answers to the query, we can still use them to deduce as many answers as possible. In many global information applications, the notion of equivalence used is often too restrictive. We propose a notion of pseudo-equivalence that allows more queries to be rewritten usefully: we show that if a query has an equivalent rewriting, the query also has a pseudo-equivalent rewriting. The converse is not true in general. In particular, when the views are conjunctive, we show that all Datalog queries...