Sperner theory
Extremal Combinatorial Problems in Relational Data Base
FCT '81 Proceedings of the 1981 International FCT-Conference on Fundamentals of Computation Theory
Describing differences between databases
CIKM '06 Proceedings of the 15th ACM international conference on Information and knowledge management
Semantic sampling of existing databases through informative Armstrong databases
Information Systems
An information-theoretic analysis of worst-case redundancy in database design
ACM Transactions on Database Systems (TODS)
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In the present paper a distance concept of databases is investigated. Two database instances are of distance 0, if they have the same number of attributes and satisfy exactly the same set of functional dependencies. This naturally leads to the poset of closures as a model of changing database. The distance of two databases (closures) is defined to be the distance of the two closures in the Hasse diagram of that poset. We determine the diameter of the poset and show that the distance of two closures is equal to the natural lower bound, that is to the size of the symmetric difference of the collections of closed sets. We also investigate the diameter of the set of databases with a given system of keys. Sharp upper bounds are given in the case when the minimal keys are 2 (or r)-element sets.