Optimization of Relational Preferences Queries
by Bernd Hafenrichter and Werner KieÃŸling.
The article provided us with an insight into personal preferences, which are often expressed as wishes: "Wishes are free, but there is no guarantee that they can be satisfied". Computer science therefore models preferences as soft constraints with a strict partial order.
The paper continues with the introduction of preference query models and mentions the languages Preference SQL and Preference XPATH. Finally it presents transformation laws for optimizing preference queries based on their formulation in the relational algebra.