📝 DBMS – Unit 1 + Unit 2 (Long Answer Questions & Answers)

 

Unit 1: Introduction to DBMS

1️⃣ Define Database, DBMS and Explain Features of DBMS

Database: Collection of logically related data stored systematically to serve multiple applications.

DBMS: Software that manages databases, allowing users to store, modify, retrieve, and manage data efficiently.

Features of DBMS:

• Data Independence: Application programs do not depend on physical data storage.

• Efficient Data Access: Uses indexes, queries to retrieve data quickly.

• Data Security: Only authorized users can access.

• Data Integrity: Maintains accuracy and consistency using constraints.

• Data Concurrency: Multiple users can access data simultaneously without conflicts.

• Backup & Recovery: Provides automatic backup and recovery in case of failure.

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2️⃣ Difference Between DBMS and File System

File System	DBMS
Data stored in files	Data stored in structured database
Redundancy & Inconsistency	Minimizes redundancy & maintains consistency
Limited data security	High-level security features
Difficult to update & manage	Easy update, retrieval, management
No support for concurrent access	Supports multiple concurrent users
Example: MS Excel	Example: MySQL, Oracle, PostgreSQL

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3️⃣ Explain DBMS Architecture

Three levels of DBMS Architecture:

1. Internal Level: Physical storage of data, low-level description.

2. Conceptual Level: Logical structure of entire database, hides physical details.

3. External Level: User views or application views of data.

Diagram:

       +----------------+
       |   External     |
       |   Views        |
       +----------------+
              |
       +----------------+
       | Conceptual     |
       | Schema         |
       +----------------+
              |
       +----------------+
       |   Internal     |
       |   Storage      |
       +----------------+

Explanation:

• External level → user interface

• Conceptual → database structure for DBMS

• Internal → physical storage details

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4️⃣ Advantages of DBMS

• Reduced data redundancy

• Data consistency & integrity

• Efficient data access via queries

• Data security & authorization

• Multi-user concurrent access

• Backup and recovery facilities

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Unit 2: ER Model & Relational Model

1️⃣ Explain Entity, Attribute, Relationship & ER Diagram

Entity: Object or thing in real world (e.g., Student, Employee)
Attribute: Property of an entity (e.g., Name, Age, Roll No)
Relationship: Association among entities (e.g., Student enrolls in Course)

ER Diagram Example:

[Student]───Enrolled_In───[Course]
   | Name                    | CName
   | RollNo                  | CID

Types of Attributes:

• Simple / Composite

• Single-valued / Multi-valued

• Derived

Types of Relationships:

• One-to-One (1:1)

• One-to-Many (1:N)

• Many-to-Many (M:N)

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2️⃣ Explain Keys in DBMS

Primary Key: Unique identifier for entity (e.g., RollNo)
Candidate Key: Possible key that can act as primary key
Foreign Key: Attribute referencing primary key of another table
Super Key: Any set of attributes that uniquely identifies entity

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3️⃣ Relational Model Concepts

Relation: Table with rows (tuples) and columns (attributes)
Tuple: Row of a table (one record)
Attribute: Column of a table (property)
Domain: Set of possible values for an attribute

Example: Student Table

RollNo	Name	Age
101	Adarsh	21
102	Riya	20

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4️⃣ Convert ER Diagram to Relational Schema

ER Diagram Example:

• Entities: Student(SID, Name), Course(CID, CName)

• Relationship: Enroll(SID, CID)

Relational Schema:

• Student(SID, Name)

• Course(CID, CName)

• Enroll(SID, CID)

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5️⃣ Advantages of ER Model

• Easy to understand for users

• Helps in database design

• Visual representation of entities, relationships

• Identifies primary keys and constraints