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Lesson Navigation IconRelationales Datenmodell

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Unit Navigation IconAbbildung ER-Schema

LO Navigation IconERM concepts

LO Navigation IconRule 1

LO Navigation IconRule 2

LO Navigation IconRule 3

LO Navigation IconRule 4

LO Navigation IconRule 5

LO Navigation IconRule 6

LO Navigation IconRule 7

LO Navigation IconRule 8

LO Navigation IconAnwendung der Regeln

LO Navigation IconUmwandlungsübung

Unit Navigation IconData integrity

Unit Navigation IconNormalisierung

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Rule 3

In this step the binary relationships of the following type (1,1)(1,1), (0,1)(1,1) or (0,1)(0,1) are transformed into the relational database scheme.

Definition rule 3

Search for all binary relationships B (1,1)(1,1), (0,1)(1,1) or (0,1)(0,1). Find the relational scheme S and T that are connected through relationship B. Choose one of them (eg. S) and insert the primary of the other relational scheme (eg. T) as a foreign key. Also add the properties of B as attributes into this relational scheme.

In this example you can see the application of rule 3:

Rule 3

A binary relationship (type (1,1)(1,1)-, (0,1)(1,1)- and (0,1)(0,1)) is chosen: leads.

Then we choose an entity set that is related to this relationship:

Newspaper(Name, Circulation, Price)

The primary key of the second entity set (eg. ChiefEditor) is inserted as foreign key in the first relational scheme:

Newspaper(Name, Circulation, Price, ChiefEditor_PersNo.)

Now the properties of the relationship are used as attributes in the relational scheme:

Newspaper(Name, Circulation, Price, ChiefEditor_PersNo., SinceDate)

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