Database Reference
In-Depth Information
2.
Fuzzy completeness constraints in the category (on the union of all superclasses):
This constraint restricts the number of instances, of all superclasses (the union), which
belong to the category. This is represented by an arc labeled with its fuzzy quantifi er,
crossing the line which joins the category with the circle. Normally, this fuzzy quan-
tifi er will be relative. For example, with the quantifi er “almost all” on the category
the constraint expresses that: “almost all elements of all superclasses belong to the
category”. This constraint allows the use of the fuzzy (min,max) notation too, indicat-
ing the minimum and maximum number of all superclasses instances which belong
to the category. Notice that this second way is always referred to as all superclasses
instances, i.e., to the union of all superclasses. This reason makes it such that relative
fuzzy quantifi ers are preferred in this constraint.
Example 10.
Let us consider four entity types for vehicles: Car, Truck, Motorbike
and Bicycle. Some vehicles may belong to the Registered Vehicle entity. Figure 10 depicts
this model with some participation constraints: Almost all cars and all trucks must be reg-
istered vehicles. Besides, the model allows a maximum of approximately fi ve bicycles to
be registered vehicles. The arc labeled with the fuzzy quantifi er Most indicates that most
motorbikes or bicycles (its union) must be registered.
On the other hand, fuzzy completeness constraint establishes that approximately half
of the existing vehicles must be registered vehicles.
FUZZY CONSTRAINTS IN
SHARED SUBCLASSES:
PARTICIPATION AND COMPLETENESS
A shared subclass (or intersection type) is a subclass with several superclasses (Elmasri
et al., 2000). Each member of the subclass must be a member of all of the superclasses,
i.e., the subclass is a subset of the intersection of all of the superclasses. A shared subclass
Figure 10: Example 10. Fuzzy constraints on a union type or category
