We consider the problem of rewriting queries using {\it only} materialized views. We first show that if the views subsume the query from the point of view of the information content, then the query can be rewritten using only the views, but the resulting query might be extremely inefficient. We then focus on aggregate views and queries over a single relation, which are fundamental in many applications such as data warehousing. We show that in this case, it is possible to guarantee that as soon as the views subsume the query, it can be rewritten in terms of the views in a simple query language. Our main contribution is the conception of rewriting algorithms which run in polynomial time, and the proof of their completeness which relies on combinatorial arguments. Finally, we consider the materialization of ratio views such as average and percentage, important for the design of materialized views.
On the content of materialized aggregate views
Tininini L
2003
Abstract
We consider the problem of rewriting queries using {\it only} materialized views. We first show that if the views subsume the query from the point of view of the information content, then the query can be rewritten using only the views, but the resulting query might be extremely inefficient. We then focus on aggregate views and queries over a single relation, which are fundamental in many applications such as data warehousing. We show that in this case, it is possible to guarantee that as soon as the views subsume the query, it can be rewritten in terms of the views in a simple query language. Our main contribution is the conception of rewriting algorithms which run in polynomial time, and the proof of their completeness which relies on combinatorial arguments. Finally, we consider the materialization of ratio views such as average and percentage, important for the design of materialized views.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
