On semantic issues connected with incomplete information databases
ACM Transactions on Database Systems (TODS)
Variations on the Common Subexpression Problem
Journal of the ACM (JACM)
A relational model of data for large shared data banks
Communications of the ACM
Null values in data base management a denotational semantics approach
SIGMOD '79 Proceedings of the 1979 ACM SIGMOD international conference on Management of data
Current, Legacy, and Invalid Tuples in Conditionally Evolving Databases
ADVIS '02 Proceedings of the Second International Conference on Advances in Information Systems
Functional Dependencies in Relational Expressions Based on Or-Sets
TSCTC '02 Proceedings of the Third International Conference on Rough Sets and Current Trends in Computing
Exploiting data dependencies with null values for ontology extraction
ER'12 Proceedings of the 31st international conference on Conceptual Modeling
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Functional dependencies play an important role in relational database design. They are defined in the context of a single relation which at all times must contain tuples with non-null entries. In this paper we examine an extension of the functional dependency interpretation to handle null values, that is, entries in tuples that represent incomplete information in a relational database. A complete axiomatization of inference rules for extended functional dependencies is also presented. Only after having such results is it possible to talk about decompositions and normalization theory in a context of incomplete information. Finally, we show that there are several practical advantages in using nulls and a weaker notion of constraint satisfiability.