Which Are My Preferred Items?

Dealing with user preferences is becoming a widespread issue in novel data-intensive application domains, such as electronic catalogs, e-commerce, multimedia databases, and real estates. Given a set of preferences, an important problem is to efficiently determine which are the “best” objects, according to such preferences. In this paper we assume that preferences are expressed in a qualitative way over the tuples of a relation schema (e.g., I prefer product A to product B), which is quite natural from the user point of view and also includes, as a proper subcase, quantitative preferences defined by means of a scoring function. Starting from an analysis of basic properties of (qualitative) preferences, we consider the Best operator, which can be used to smoothly embed preferences in queries of relational algebra. We study general properties of this operator and present a practical algorithm for its computation. We show how the algorithm improves the simple nested-loops approach and can lead to faster response times.