Preference queries in deductive databases

摘要: Traditional database query languages such as datalog and SQL allow the user to specify only mandatory requirements on data be retrieved from a database. In many applications, it may natural express not but also preferences retrieved. Lacroix Lavency10) extended with notion of preference showed how resulting language could still translated into domain relational calculus. We explore use in databases setting datalog. introduce formalism programs (PDPs) logic without uninterpreted function symbols for this purpose. PDPs extend constructs which predicate is optimized criterion optimization relaxed used relaxation. can show that all soft Reference10) directly encoded PDP. first develop anaively-pruned bottom-up evaluation procedure sound complete computing answers normal relaxation queries when are stratified, we then scheme case necessarily finally an extension themagic templates method datalog14) equivalent more efficient program evaluation.