A simplied universal relation assumption and its properties
ACM Transactions on Database Systems (TODS)
The theory of joins in relational databases
ACM Transactions on Database Systems (TODS)
Testing implications of data dependencies
ACM Transactions on Database Systems (TODS)
Multivalued dependencies and a new normal form for relational databases
ACM Transactions on Database Systems (TODS)
On the Desirability of Acyclic Database Schemes
Journal of the ACM (JACM)
Principles of Database Systems
Principles of Database Systems
CAAP '83 Proceedings of the 8th Colloquium on Trees in Algebra and Programming
Acyclic Database Schemes (of Various Degrees): A Painless Introduction
CAAP '83 Proceedings of the 8th Colloquium on Trees in Algebra and Programming
Properties of acyclic database schemes
STOC '81 Proceedings of the thirteenth annual ACM symposium on Theory of computing
On the complexity of join dependencies
ACM Transactions on Database Systems (TODS)
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In [9] we proposed a method for decomposing join dependencies (jd's) in a relational database. Decomposing a jd can be useful for separating cyclic and acyclic parts of jd's, obtaining more insight in the structure of a jd or making integrity-checking more efficient. The decomposition methodology of [9] has many desirable properties. However, in general it cannot generate all the decompositions of a given jd. In this paper, we first recall this decomposition methodology and its most important properties. We then introduce a subclass of jd's, the unambiguous jd's. We show that this class represents exactly those jd's that have a unique decomposition (which can be obtained by our method). We also give a characterization of this decomposition in terms of the structure of the original jd. To prove our results, we make extensive use of hypergraph theory.