Generalization in database management system: 26 MCQs with answers

The process of defining a more general entity type from a set of more specialized entity types.

Generalization is a top-down approach in ER modeling where common attributes of multiple entity types are abstracted into a higher-level (superclass) entity type.

From subclass to superclass

Generalization proceeds from specialized entity types (subclasses) upward to a more general entity type (superclass), identifying commonalities.

Superclass

The higher-level entity type resulting from generalization is the superclass, while the specialized types are subclasses.

Subclasses inherit attributes and relationships from the superclass.

In generalization, subclasses automatically have all the attributes and relationships of the superclass, which is known as inheritance.

False

Generalization is a bottom-up process, combining subclasses into a superclass. Specialization is top-down.

False

Disjoint means an entity can belong to at most one subclass, not multiple.

Defining 'Vehicle' as a superclass of 'Car' and 'Truck'

Generalization identifies common features of 'Car' and 'Truck' to form a more general 'Vehicle' entity type. The other options do not represent generalization.

To capture commonalities among entity types and simplify the model

Generalization helps in abstracting common attributes and relationships, making the model cleaner and reducing duplication in the schema.

An entity can belong to at most one subclass.

A disjoint constraint specifies that an entity instance can be a member of at most one of the subclasses in the generalization.

Completeness

Completeness (or total specialization) requires that every superclass entity belongs to at least one subclass; partial specialization allows some entities to not belong to any subclass.

Total specialization

Total specialization means the superclass is completely covered by its subclasses; every superclass entity is also a member of some subclass.

Cardinality

Cardinality is a constraint on relationships, not on generalization. Disjointness, completeness, and overlap are constraints that apply to generalization/specialization.

Can belong to multiple subclasses simultaneously

Overlapping generalization allows an entity to be a member of more than one subclass at the same time.

An employee can be either a manager or a worker, but not both.

Disjoint means no overlap; an employee cannot be both a manager and a worker in this classification.

Generalization is bottom-up, specialization is top-down.

Generalization is a bottom-up process (combining subclasses into a superclass), while specialization is top-down (dividing a superclass into subclasses).

It reduces redundancy by storing common attributes once.

By placing common attributes in the superclass, generalization avoids repeating them in each subclass, thus reducing redundancy.

Person -> Student, Employee

Person is a superclass with Student and Employee as subclasses, representing a generalization hierarchy.

Every superclass entity must belong to at least one subclass.

Total specialization means that the superclass is completely covered by its subclasses; every superclass entity is also a member of some subclass.

Partial specialization

Partial specialization allows some superclass entities to not be members of any subclass.

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1 mark for correct definition of generalization (bottom-up, combining subclasses into superclass). 1 mark for correct definition of specialization (top-down, dividing superclass into subclasses). 1 mark for clear explanation of the difference (direction and purpose). 1 mark for a valid real-world example of generalizat…

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1 mark for explaining disjointness with example. 1 mark for explaining overlap with example. 1 mark for explaining total completeness with example. 1 mark for explaining partial completeness with example. 1 mark for clarity and organization. 1 mark for overall correctness.

A person can be both a student and an employee.

Overlapping allows an entity to be in multiple subclasses; a person can be both a student and an employee, so it is overlapping.

By creating a single table for the superclass and separate tables for each subclass with foreign keys referencing the superclass.

A common mapping strategy is to create a table for the superclass and tables for each subclass, linking them via foreign keys (often using the primary key of the superclass).

It can lead to complex queries when joining multiple tables.

Generalization can result in multiple tables that need to be joined to retrieve complete information, potentially complicating queries.

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1 mark for describing the single table strategy. 1 mark for its advantages and disadvantages. 1 mark for describing the superclass/subclass tables strategy. 1 mark for its advantages and disadvantages. 1 mark for describing the only subclass tables strategy. 1 mark for its advantages and disadvantages.

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1 mark for correctly identifying the superclass and subclasses. 1 mark for identifying the overlapping and partial constraints. 1 mark for describing the Person table. 1 mark for describing the Student and Employee tables with foreign keys. 1 mark for explaining how the implementation supports overlapping and partial c…