Databases Reference
In-Depth Information
In the logical data model, many-to-many bi-directional
associations must be avoided as they can become complex to
interpret at the ergonomic level. We prefer instead to
establish an orientation, that which is most natural for the
user, even if it is not specified at the semantic modeling
level. In Figure 10.3, the association is oriented from Class A
to Class B which defines the direction to browse the link.
Semantic modeling
Logical modeling
InfoC l as sA
lstIdClassesB [*] : real
Data Category #1
Data Category #2
Figure 10.3.
Derivation of a many-to-many association
spanning two data categories
10.5.2.2.
Qualifier attribute
The qualifier attribute enables class occurrences “ClassB”
to be filtered through the association starting from ClassA.
This is an enumeration data type. In this case, the logical
modeling brings a composite foreign key (in this example:
InfoRole2FK).
This derivation rule does not depend on the frontiers of
data categories.
