E-R Model Questions and Answers

1. Define the Entity-Relationship (E-R) Model.

The E-R model represents data as entities, attributes, and relationships, providing a conceptual

framework for database design.

2. What is a key attribute in an entity set?

A key attribute uniquely identifies an entity in an entity set, such as a Student ID in a Student entity

set.

3. Define a strong entity set.

A strong entity set is an independent entity that can exist without relying on any other entity, having

its own primary key.

4. What is a weak entity in an E-R model?

A weak entity depends on a strong entity for its existence and lacks a primary key, relying on a

foreign key as part of its identifying relationship.

5. What is the purpose of an E-R diagram?

An E-R diagram visually represents the structure of a database, illustrating entities, attributes, and

relationships.

6. What are constraints in a database?

Constraints are rules enforced to maintain data integrity and accuracy, such as primary key, foreign

key, and unique constraints.

7. What is the difference between a primary key and a foreign key?

A primary key uniquely identifies a record, while a foreign key links two tables by referencing the

primary key of another table.

8. Define multiplicity in the context of E-R diagrams.

Multiplicity defines the number of instances of one entity associated with another, such as
one-to-one, one-to-many, or many-to-many relationships.

9. What is the role of attributes in an E-R model?

Attributes define properties of entities or relationships, such as a Customer entity having attributes

like Name, Address, and Contact.

10. Define Candidate key with a suitable example.

A candidate key is an attribute or set of attributes that can uniquely identify a record. For example, in

a Student table, both Student ID and Email can be candidate keys.

1. Explain the entire database design process, from conceptual to logical design.

The database design process involves the following steps:

- **Conceptual Design:** Identify entities, attributes, and relationships using E-R diagrams.

- **Logical Design:** Convert the E-R model into a relational schema with tables, keys, and

constraints.

- **Physical Design:** Optimize storage and access mechanisms based on database usage.

2. Discuss the purpose and importance of E-R diagrams in database design.

E-R diagrams provide a clear and visual representation of database structure, helping stakeholders

understand entities, attributes, and relationships. They are crucial for effective database planning

and communication.

3. Define the various types of relationships (one-to-one, one-to-many, many-to-many) in E-R

diagrams with examples.

- **One-to-One:** A student has one ID card, and an ID card belongs to one student.

- **One-to-Many:** A teacher can teach multiple students, but each student has one teacher.

- **Many-to-Many:** Students enroll in many courses, and each course has many students.

4. Distinguish between ER Model and Relational Model.

- **ER Model:** Focuses on entities and relationships at a conceptual level using diagrams.
- **Relational Model:** Represents data as structured tables with rows and columns for

implementation.

5. Explain constraints and its types with a suitable example.

- **Entity Integrity Constraint:** Ensures primary key uniqueness and non-null values.

- **Referential Integrity Constraint:** Maintains consistency between foreign and primary keys.

- **Domain Constraint:** Restricts data values within a valid range, e.g., age > 0.

6. Describe how multi-valued and composite attributes are handled in E-R diagrams.

- **Multi-valued Attributes:** Represented as separate entities with relationships to the main entity.

- **Composite Attributes:** Broken down into simpler attributes, such as FullName split into

FirstName and LastName.

7. Explain how generalization and specialization are used in advanced E-R modeling.

- **Generalization:** Combines similar entities into a single generalized entity.

- **Specialization:** Divides a general entity into specific sub-entities based on attributes.

8. Discuss the different types of constraints (entity integrity, referential integrity, and domain

constraints) with examples.

- **Entity Integrity:** Each row in a table must have a unique, non-null primary key.

- **Referential Integrity:** Foreign key values must match primary key values in another table.

- **Domain Constraint:** Attribute values must conform to predefined rules, e.g., salary > 0.

9. Explain how weak entities are represented in E-R diagrams and the role of identifying

relationships.

Weak entities are represented with a double rectangle, and identifying relationships are denoted by

a double diamond. They rely on strong entities for identification.

10. Differentiate between weak and strong entity sets with a suitable example.

- **Strong Entity Set:** Independent, with a primary key (e.g., Employee).

EmployeeDependents).