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Database Relations with Null Values

By Carlo Zaniolo


this paper we briefly review some of these issues and then concentrate on the problem of generalizing the formal framework of the relational data model to include null values. A basic problem with null values is that they have many plausible interpretations. The ANSI/SPARC interim report, for instance, cites 14 different manifestations of nulls. Most authors, however, agree that the various manifestations of nulls can be reduced to two basic interpretations. These are: (a) the unknown interpretation: a value exists but it is not known; and lb) the nonexistent interpretation: a value does not exis

Year: 1984
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