Abstract
In the previous chapters we have usually assumed that tuples are complete, i. e. that a tuple of a relation instance has, for each attribute of the relation scheme, a value of the domain of that attribute. In a “real” database however it is sometimes necessary to insert a new tuple into an instance, although the value of that tuple for some attributes is (still) unknown. In Example 1.10 we said that if a stay is not yet finished, the LEAV-DATE-value of a tuple is unknown. The definition of a relation instance (Definition 1.4) however does not allow the use of unknown unless this is a “normal” element of the domain of the attribute LEAV-DATE.
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© 1989 Springer-Verlag Berlin Heidelberg
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Paredaens, J., De Bra, P., Gyssens, M., Van Gucht, D. (1989). Incomplete Information. In: The Structure of the Relational Database Model. EATCS Monographs on Theoretical Computer Science, vol 17. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-69956-6_6
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DOI: https://doi.org/10.1007/978-3-642-69956-6_6
Publisher Name: Springer, Berlin, Heidelberg
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