Explore the intricacies of querying databases with incomplete information. This paper delves into the semantic challenges of interpreting queries when dealing with databases containing uncertainties and partial data. It introduces a model that represents incomplete information using subsets of attribute domains, extending Codd’s null value concept. The research examines a simple query language designed for communicating with such systems, defining its semantics precisely. It distinguishes between external interpretations, which directly relate queries to the real-world, and internal interpretations, which refer to the system’s information about the world. Both interpretations are provided with axiom sets for query transformations. Equivalent query transformations are exploited for query evaluation, offering insights into how to effectively retrieve information from incomplete databases. This work contributes to the foundations of database theory and has implications for the design of more robust and user-friendly information systems.
Published in ACM Transactions on Database Systems, this paper addresses core issues in database theory and management, fitting squarely within the journal's focus. The research on incomplete information and query semantics aligns with the journal's emphasis on foundational topics in database systems. Its exploration of query transformations and evaluation techniques is relevant to the design of efficient database systems.