On the Equivalence of Database Models

All eqmvalence is estabhshed between network databases and a subclass of relational databases. A database is a set of files together w~th a set of constraints that the fdes must satisfy. The constraints are spectfied by Bachman diagrams m the network model and by data dependencies m the relational model. The subclass of relatmnal databases of interest ~s characterized by the absence of two properties of data dependencies: conflzct and contention It is proved that network databases with loop-free Bachman diagrams are eqmvalent to relational databases which are free of conflicts and contenUons. When its Bachman dmgram has loops, a network database ts equivalent to a collection of relattonal databases in this subclass. Th~s study of equivalence is also related to database design algorithms. Although the network model cannot capture the nouons of conflict and contention, they are the source of several problems which have been observed in the decomposiuon approach to relational database design, notably the split key problem, the nonumqueness problem, and lossy joins It is shown that the decomposition approach can be apphed to conflictand contention-free relational databases without any of these problems. The results serve as a theorettcal foundatton for database translatton between different models and for designing multimodel database management systems. Categortes and Subject Descriptors: H.2.1[DatabaseManagement|'LoglcalDestgn--datamodels;H2.5 [Database Management]" Heterogeneous Databases--data translation General Terms: Algorithms, Design, Theory Addmonal

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