### Abstract

Original language | English |
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Title of host publication | The Theory of Databases |

Editors | P.C. Kanellakis |

Place of Publication | Greenwich CT |

Publisher | JAI Press |

Pages | 69-106 |

ISBN (Print) | 0-89232-611-5 |

Publication status | Published - 1986 |

### Publication series

Name | Advances in Computing Research |
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Volume | 3 |

ISSN (Print) | 0741-9341 |

### Fingerprint

### Cite this

*The Theory of Databases*(pp. 69-106). (Advances in Computing Research; Vol. 3). Greenwich CT: JAI Press.

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*The Theory of Databases.*Advances in Computing Research, vol. 3, JAI Press, Greenwich CT, pp. 69-106.

**On the decomposition of join dependencies.** / Gyssens, M.; Paredaens, J.

Research output: Chapter in Book/Report/Conference proceeding › Chapter › Academic › peer-review

TY - CHAP

T1 - On the decomposition of join dependencies

AU - Gyssens, M.

AU - Paredaens, J.

PY - 1986

Y1 - 1986

N2 - In an earlier paper we proposed an algorithm for decomposing join dependencies (jds) in a relational database, using "hinges." Decomposing a jd can be useful for separating cyclic and acyclic parts of jds, obtaining more insight into the structure of a jd or making integrity checking more efficient. The Hinge Decomposition Algorithm has many desirable properties. However, in general it cannot generate all the decompositions of a given jd. Hence we cannot be sure that the Hinge Decomposition Algorithm generates the decomposition that is most suitable for the purposes it has to serve. Therefore, after reviewing the Hinge Decomposition Algorithm and its most important properties, we introduce unambiguous jds. We show that decomposable unambiguous jds are characterized by the property that they have exactly one decomposition satisfying some elementary desirable properties (union and intersection properties). Furthermore, this decomposition can be obtained with the Hinge Decomposition Algorithm. Finally, we characterize this decomposition in terms of the structure of the original jd. To prove our results, we make extensive use of hypergraph theory.

AB - In an earlier paper we proposed an algorithm for decomposing join dependencies (jds) in a relational database, using "hinges." Decomposing a jd can be useful for separating cyclic and acyclic parts of jds, obtaining more insight into the structure of a jd or making integrity checking more efficient. The Hinge Decomposition Algorithm has many desirable properties. However, in general it cannot generate all the decompositions of a given jd. Hence we cannot be sure that the Hinge Decomposition Algorithm generates the decomposition that is most suitable for the purposes it has to serve. Therefore, after reviewing the Hinge Decomposition Algorithm and its most important properties, we introduce unambiguous jds. We show that decomposable unambiguous jds are characterized by the property that they have exactly one decomposition satisfying some elementary desirable properties (union and intersection properties). Furthermore, this decomposition can be obtained with the Hinge Decomposition Algorithm. Finally, we characterize this decomposition in terms of the structure of the original jd. To prove our results, we make extensive use of hypergraph theory.

M3 - Chapter

SN - 0-89232-611-5

T3 - Advances in Computing Research

SP - 69

EP - 106

BT - The Theory of Databases

A2 - Kanellakis, P.C.

PB - JAI Press

CY - Greenwich CT

ER -