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NULL-Werte und dreiwertige Logik in SQL

Authors: Günter Matthiessen;

NULL-Werte und dreiwertige Logik in SQL

Abstract

In relationalen Datenbanken ist es ublich, das gewisse Felder „NULL“ sein konnen (vgl. [Date86]). Wir sagen hier bewust nicht „den Wert NULL haben“. NULL kann u.a. bedeuten, das der aktuelle Wert eines Attributs unbekannt ist. Andere Arten von Nullen, wie z.B. „nicht anwendbar“ oder „gibt es nicht“ werden hier nicht behandelt, (vgl. dazu [Codd86] und [Codd87]).

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
0
Average
Average
Average
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