Chapter 4: Problem 6

Discuss the two main types of constraints on specializations and generalizations.

Short Answer

Expert verified

The two main types of constraints on specializations and generalizations are disjoint and completeness constraints. Disjoint constraint asserts that each instance of the superclass can be only one of the subclasses. Completeness constraint indicates if each instance in the superclass must belong to some subclass (total) or may not belong to any subclass (partial).

Step by step solution

Understanding Specializations and Generalizations

In the database model, specialization is a process of defining a set of subclasses for a given entity type. Each subclass has distinct attributes or relationships of their own. On the other hand, generalization is the reverse process of specialization, resulting in an entity type with common properties. It basically consists of higher and lower-level entity sets.

Defining Disjoint Constraint

Under the disjoint constraints, each entity can belong to only one lower-level entity set. It means an instance of a superclass can be only one of the subclasses. Disjoint is also known as mutually exclusive, denoted as 'd' in ER diagrams.

Defining Completeness Constraint

The completeness constraint indicates whether an instance of a superclass should belong to at least one of its subclasses. There are two types of completeness constraints - total and partial. In total completeness, every instance in the superclass must belong to some subclass. In partial completeness, some instances in the superclass may not belong to any subclass.

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Discuss the two main types of constraints on specializations and generalizations.

Short Answer

Step by step solution

Understanding Specializations and Generalizations

Defining Disjoint Constraint

Defining Completeness Constraint

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