Qualiied Answers That Reeect User Needs and Preferences

This paper introduces a formalism to describe the needs and preferences of database users. Because of the precise formulation of these concepts, we have found an automatic and very simple mechanism to incorporate user needs and preferences into the query answering process. In the formalism, the user provides a lattice of domain independent values that deene preferences and needs and a set of domain speciic user constraints qualiied with lattice values. The constraints are automatically incorporated into a relational or deductive database through a series of syntactic transformations that produces an annotated deductive database. Query answering procedures for deductive databases are then used, with minor modiications, to obtain annotated answers to queries. Because preference declaration is separated from data representation and management, preferences can be easily altered without touching the database. Also, the query language allows users to ask for answers at diierent preference levels. An extended example shows how these methods are used to handle large quantities of DNA sequence data. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the VLDB copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Very Large Data Base Endowment. To copy otherwise, or to republish, requires a fee and/or special permission from the Endowment.