Optimization of Preference Queries under Hard Sum Constraints

Many important applications, e.g. planning tasks, de-mand the flexible and efficient use of personaliza-tion and preference handling techniques. Apply-ing preference-based search technology could improve things quite a lot, e.g. using Preference SQLwhere pref-erences (i.e. soft constraints) can be combined with hard constraints. However, there are still fundamental effi-ciency issues that need to be addressed. In this paper we study preference database queries involving hard con-straints over the sum of multiple attributes. We develop algebraic optimization techniques to transform a prefer-ence query with a sum constraint in order to enable its efficient processing by database engines. For this pur-pose we present new transformation laws for an efficient solution of this problem