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Assumptions in relational database theory

Assumptions in relational database theory,10.1145/588111.588113,Paolo Atzeni,Douglas Stott Parker Jr.

Assumptions in relational database theory   (Citations: 50)
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Many results in relational database theory on the structure of dependencies, query languages, and databases in general have now been established. However, neither (a) the reliance of these results on various assumptions, nor (b) the desirability or reasonableness of these assumptions themselves have been closely examined. These assumptions are nontrivial: examples include the universal relation assumption and the lossless join assumption.The purpose of the present paper is to clarify many of the existing assumptions, and point out weaknesses. This is desirable both to harden the statements of previous results, and to evaluate recent suggestions that certain assumptions (such as the acyclic JD assumption) may be useful for modeling "real world" databases. Specifically, studies are made of assumptions made for (1) universal relations, (2) functional dependency inference, and (3) decomposition theory. We show that:• Some assumptions (such as uniqueness of relationships among attributes) can be more powerful than they appear;• common treatment of FDs is sometimes inappropriate, and for example FD inferences such as {A → B, B → C} |= A → C can be incorrect;• the 'decomposition' approach to design may be hard to justify in real terms; and• Acyclic JDs may have drawbacks in eliminating ambiguity in queries and in modeling real enterprises.It is hoped that this exposition will help clarify some confusing issues in this field, and will lead to a better understanding of which assumptions are reasonable and useful in modeling the "real world".
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    • ...Atzenti and Parker [1] advise against it; Markowitz and Shoshani [15] feel that it is not harmful if it is done right...

    Don Goelmanet al. Entity-Relationship Modeling Re-revisited

    • ...ambiguity problem and, possibly, a misunderstanding of the UR data model at its early stage of development caused debates among several researchers [1,11,28,29,47,48] concerning the usefulness of the application of this approach...

    Yao-chuan Tsai. The Theory of SML Schema-Directed Query

    • ...Thus, different authors reach contradictory results concerning the possibility of such a combination, namely that it can be achieved (1) by first restructuring the ER schema [4]; (2) without restricting the ER schema allowed [11]; and (3) by applying certain restrictions on the ER schema allowed [2]...
    • ...Unlike Jajodia et al. [11], Atzeni and Parker [2] contend that only ER...

    Victor M. Markowitzet al. Representing extended entity-relationship structures in relational dat...

    • ...In the schema of figure l(ii), for example, since DATE characterizes...
    • ...Indeed, it can be shown that the schema of figure l(iii) together with the inclusion dependencies of figure l(iv) provide a correct representation for the ER structure of figure l(i)...
    • ...Let object-set 0; be the aggregation of object-sets Oij , l<j<m, and let each objectrset Oij be represented by relation-scheme Ri, ( Yij), 12 jlm, respectively...
    • ...Indeed, the correct representations for the ER structures of figures l(i) and 7(i) are not equivalent in the sense defined in this paper...

    Victor M. Markowitzet al. On the Correctness of Representing Extended Entity-Relationship Struct...

    • ...In the schema of figure l(ii), for example, since DATE characterizes...
    • ...Indeed, it can be shown that the schema of figure l(iii) together with the inclusion dependencies of figure l(iv) provide a correct representation for the ER structure of figure l(i)...
    • ...Let object-set 0; be the aggregation of object-sets Oij , l<j<m, and let each objectrset Oij be represented by relation-scheme Ri, ( Yij), 12 jlm, respectively...
    • ...Indeed, the correct representations for the ER structures of figures l(i) and 7(i) are not equivalent in the sense defined in this paper...

    Victor M. Markowitzet al. On the correctness of representing extended entity-relationship struct...

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