Database Reference
In-Depth Information
F
IGURE
7.6
The entities for Mountain View Music, with primary keys
Modeling Cardinality
Recall that in Chapter 2 we discussed the cardinality of relationships. We
explained the differences between one-to-many and zero-or-one-to-many
relationships. As you add the relationships to your data model, you need to
specify exactly which cardinality each relationship has at a granular level.
In particular, you need to evaluate each relationship to determine its car-
dinality and notate it in the modeling software. If you omit the granular-
level definition, the software usually chooses a default for you, which, in
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