Concept Notes
1. Entity Relationship (ER) Model
- A high-level conceptual model for database design.
- Represents real-world entities and their relationships.
Key Components:
- Entity → Object in real world (e.g., Student, Course).
- Attributes → Properties of entity (e.g., RollNo, Name).
- Key Attribute → Uniquely identifies entity (e.g., RollNo).
- Relationship → Association between entities (e.g., Student–Enrolls–Course).
- Cardinality → 1:1, 1:N, M:N.
Example:
- Entity: Student (RollNo, Name, Age)
- Entity: Course (CourseID, Title)
- Relationship: Enrolls (between Student & Course)
2. Relational Model
- Proposed by E.F. Codd (1970).
- Data is represented in the form of relations (tables).
Key Concepts:
- Relation: Table with rows (tuples) and columns (attributes).
- Tuple: A single row.
- Attribute: Column of relation.
- Domain: Set of valid values for attribute.
- Degree: Number of attributes in a relation.
- Cardinality: Number of tuples in a relation.
3. Mapping ER → Relational Model
- Entity → Relation (table).
- Attributes → Columns.
- Relationship → Relation (with foreign keys).
- Weak entity → Relation including owner’s primary key.
⚙️ Formulas (QuickLaTeX)
🔟 10 MCQs – GATE 2026 DBMS (ER & Relational Model)
Q1. In ER model, attributes that uniquely identify entity instances are called:
A) Foreign keys
B) Primary keys
C) Super attributes
D) Derived attributes
Q2. The mapping of a many-to-many relationship in ER model leads to:
A) A single table with merged attributes
B) Two tables only
C) A new relation with foreign keys of both entities
D) No relation needed
Q3. Which of the following is NOT an attribute type in ER model?
A) Simple
B) Composite
C) Multivalued
D) Indexed
Q4. In relational model, the number of attributes in a relation is called:
A) Degree
B) Cardinality
C) Domain
D) Tuple
Q5. In relational model, which operation ensures no duplicate tuples?
A) Join
B) Projection
C) Union
D) Selection
Q6. A weak entity must always have:
A) Multivalued attribute
B) Derived attribute
C) Partial key and owner entity
D) Composite key only
Q7. In relational schema R(A,B,C,D), total number of possible candidate keys is determined by:
A) Cardinality
B) Degree
C) Functional dependencies
D) Number of tuples
Q8. Which of the following is true for relational model?
A) Tuples are ordered
B) Attributes are ordered
C) Domains can be composite
D) Tuples are unordered
Q9. If a relation has 5 attributes, what is its degree?
A) 5
B) Depends on tuples
C) Infinite
D) Cannot be determined
Q10. Which ER diagram relationship represents “One student enrolls in many courses, and each course has many students”?
A) 1:1
B) 1:N
C) M:N
D) None
✅ Answer Key
| Q.No | Answer |
|---|---|
| 1 | B |
| 2 | C |
| 3 | D |
| 4 | A |
| 5 | C |
| 6 | C |
| 7 | C |
| 8 | D |
| 9 | A |
| 10 | C |
🧠 Explanations
- Unique attributes = Primary key.
- M:N relation → new relation with foreign keys of both.
- Indexed is a storage structure, not attribute type.
- No. of attributes = Degree.
- Union removes duplicates.
- Weak entity needs partial key + owner’s PK.
- Candidate keys depend on functional dependencies.
- Tuples are unordered in relational model.
- 5 attributes → degree = 5.
- Student–Course = Many-to-Many (M:N).
🎯 Why This Practice Matters
- ER & Relational models are the foundation of DBMS.
- Every year, 2–3 GATE questions are directly asked from ER mapping & relational basics.
- Strong clarity helps in Normalization, SQL queries, and Database design.
- Also important for interviews (system design, schema design).
📲 CTA
👉 Join our GATE 2026 DBMS Prep Telegram Group for daily MCQs & solutions: @LearnNewThingsHub
