PREFER

Abstract

Users often need to optimize the selection of objects by appropriately weighting the importance of multiple object attributes. Such optimization problems appear often in operations' research and applied mathematics as well as everyday life; e.g., a buyer may select a home as a weighted function of a number of attributes like its distance from office, its price, its area, etc. We capture such queries in our definition of preference queries that use a weight function over a relation's attributes to derive a score for each tuple. Database systems cannot efficiently produce the top results of a preference query because they need to evaluate the weight function over all tuples of the relation. PREFER answers preference queries efficiently by using materialized views that have been pre-processed and stored. We first show how the result of a preference query can be produced in a pipelined fashion using a materialized view. Then we show that excellent performance can be delivered given a reasonable number of materialized views and we provide an algorithm that selects a number of views to precompute and materialize given space constraints. We have implemented the algorithms proposed in this paper in a prototype system called PREFER, which operates on top of a commercial database management system. We present the results of a performance comparison, comparing our algorithms with prior approaches using synthetic datasets. Our results indicate that the proposed algorithms are superior in performance compared to other approaches, both in preprocessing (preparation of materialized views) as well as execution time.