Entity-Relationship (ER) Model : MCQs & PYQs with Explanation

Option C

In E–R (Entity–Relationship) modelling, a relationship represents an association among entities. Relationships are classified according to the number of participating entities.

A quaternary relationship involves four different entities participating together in a single relationship.
For example, if we have four entities such as Student, Teacher, Subject, and Classroom, and all four entities participate together in a single relationship, then it is called a quaternary relationship.

Option D

In ER-to-relational mapping, each entity set becomes a separate table. Therefore, entities A and B require two tables.
For relationships:
A one-to-many (1:N) relationship (R1) can be implemented by adding the primary key of entity A as a foreign key in table B, so no separate table is required.
A many-to-many (M:N) relationship (R2) cannot be represented using a foreign key alone, so it requires a separate relation, containing the primary keys of A and B.
Thus, total 3 tables required:

• Table for A.
• Table for B.
• Table for R2.

Option A

In India, each person has only one Aadhaar Card, and each Aadhaar number belongs to only one person.

• Each person can possess only one unique Aadhaar Card.
• Each Aadhaar Card corresponds to exactly one person.

This is a One-to-One (1:1) relationship in the ER Model.

Option A

In a one-to-many relationship, one record in the parent table can be associated with multiple records in the child table. The foreign key is placed in the child table to reference the primary key of the parent table.
In this case, one author can write many books, so the authors table is the parent table and the books table is the child table. Therefore, the foreign key referencing the author’s primary key should be stored in the “books” table.

Option C

A derived attribute is an attribute whose value can be calculated from other stored attributes.

• Age can be derived from Date of Birth.
• Year of services can be derived from Date of Joining.

Option B

In E-R modeling, cardinality defines how many instances of one entity can be associated with instances of another entity.
The statement says, “an entity appears in not more than 5 relationships” this means, one instance of an entity can be related to maximum 5 instances of another entity. This represents a 1:5 relationship.

Option A

A composite attribute is an attribute that can be divided into smaller sub-attributes.
Address can be broken into House No, Street, City, State, and PIN Code, so it is a composite attribute.
Age, City and State are the simple attributes and cannot be meaningfully divided further.

Option B

Generalization is a bottom-up approach where lower-level entities are combined to form a higher-level, more general entity. 

• For example, combining Student and Teacher into a general entity Person.

Specialization is a top-down approach, where a higher-level entity is divided into lower-level entities. 

• For example, Employee is a general entity. It is specialized into Teaching_Employee and Non_Teaching_Employee based on the type of work. This is called specialization because we move from general to specific.

Option A

E-R modeling is primarily a Top-Down approach to database design. It starts with identifying high-level entities and relationships in the real world and then gradually breaks them down into attributes and detailed structures.

Option C

When an E-R model is converted into a relational database, the goal is to represent all data and relationships in the form of tables while maintaining data integrity.
Entities are directly mapped to tables, where:

• Each Entity : Table.
• Each Attribute : Column.

Relationships are handled based on their type:

• 1:1 Relationship : Can be implemented using a foreign key in either table.
• 1:N Relationship : Foreign key is added on the “many” side.
• M:N Relationship : Must be converted into a separate table (called a junction table), which contains foreign keys of both entities.

Note:

• Weak Entities : Become tables and include foreign key of owner entity.
• Composite Attributes : Broken into individual columns.
• Multivalued Attributes : Create a separate table.
• Derived Attributes : Usually not stored in table.