Generating Efficient Plans for Queries Using Views

We study the problem of generating e cient, equivalent rewritings using views to compute the answer to a query. We take the closed-world assumption, in which views are materialized from base relations, rather than views describces in terms of abstract predicates, as is common when the open-world assumption is used. In the closedworld model, there can be an in nite number of di erent rewritings that compute the same answer, yet have quite di erent performance. Query optimizers take a logical plan a rewriting of the query as an input, and generate e cient physical plans to compute the answer. Thus our goal is to generate a small subset of the possible logical plans without missing an optimal physical plan. We rst consider a cost model that counts the number of subgoals in a physical plan, and show a search space that is guaranteed to include an optimal rewriting, if the query has a rewriting in terms of the views. We also develop an e cient algorithm for nding rewritings with the minimu...

• Type: Conference
• Year: 2001
• Where: SIGMOD
• Authors: Foto N. Afrati, Chen Li, Jeffrey D. Ullman
• Keywords: Database, Di Erent Rewritings, Optimal Physical Plan, Optimal Rewritings, SIGMOD 2001