What are the constraints on specialization and generalization?
What are the constraints on specialization and generalization?
There are three constraints that may apply to a specialization/generalization: membership constraints, disjoint constraints and completeness constraints.
What do you mean by specialization and generalization?
Definition. Specialization and generalization are main principles of database modeling. Specialization is based on a refinement of types or classes to more specific ones. Generalization maps or groups types or classes to more abstract or combined ones.
What do you mean by Disjointness constraint of generalization?
Disjoint – The requirement of this constraint is that an entity should not belong to no more than one lower-level entity set.
What is disjoint constraints in database?
• Disjoint constraint. – Describes the relationship between. members of the subclasses and indicates whether it is possible for a member of a superclass to be a member of one, or more than one, subclass.
Which of the following is not a generalization constraint?
Which of the following is not a generalization constraint? Explanation: Machine definition is not a generalization constraint. Condition defined, user defined, disjoint and overlapping are 4 generalization constraints.
What is an overlapping constraint?
In a disjoint constraint you would have to put the musician in either one or the other sub classes. In an overlapping constraint the musician can be put in both. This is a disjoint constraint situation because a bank account can either be Savings or Current. It cant be both at the same time.
What is mean specialization generalization and aggregation?
Generalization, Specialization and Aggregation in ER model are used for data abstraction in which abstraction mechanism is used to hide details of a set of objects. Generalization – Generalization is the process of extracting common properties from a set of entities and create a generalized entity from it.
What is a generalization specialization hierarchy?
A generalization hierarchy (also called is-a hierarchy) connects a superclass and one or more subclasses, representing a specialization of the superclass. Each class is defined as the specialization of at most one superclass. In technical terms, “multiple inheritance” is avoided.
What is Disjointness constraint example?
If the value of a discriminator is not null and appears in supertype entity instance then that must be linked with the only one subtype. This is called disjoint constraint. For example, you say in school a person can be teacher and student but a teacher can’t be a student and vice versa.
Which of the following are types of constraints on specialization * Membership constraint disjoint constraint completeness constraint all of the above?
Online Test
| 183. | The hierarchy in which each subclass participates in one subclass relationship is classified as |
|---|---|
| a. | specialization hierarchy |
| b. | generalization hierarchy |
| c. | jointness hierarchy |
| d. | disjoint hierarchy |
What are the constraints on generalizations and specializations?
Generalizations and specializations can have two types of constraints: (i) the disjoint/overlap relationship constraint, and, (ii) participation constraints – total or partial.
What is a total specialization constraint in SQL Server?
A total specialization constraint specifies that every entity in the superclass must be a member of at least one subclass in the specialization. For example, if every EMPLOYEE must be either an HOURLY_EMPLOYEE or a SALARIED_EMPLOYEE, then the specialization {HOURLY_EMPLOYEE, SALARIED_EMPLOYEE} in Figure 8.1 is a total specialization of EMPLOYEE.
What is the difference between generalization and specialization?
In Generalization, the difference and similarities between lower entities are ignored to form a higher entity. In Specialization, a higher entity is split to form lower entities. There is no inheritance in Generalization. There is inheritance in Specialization.
Can We have multiple specializations on an entity type?
In general, we may have several specializations defined on the same entity type (or superclass), as shown in Figure 8.1. In such a case, entities may belong to subclasses in each of the specializations.
