DBMS Topics
HubUnit 1 — Introduction to DBMS & Entity-Relationship ModelAdvantages and Disadvantages of DBMSAggregationCharacteristics of DBMSData IndependenceData ModelsDatabase Users and AdministratorsDBMS LanguagesER DiagramsEntity-Relationship ER ModelIntroduction to DBMSKeys in DBMSRelationships and CardinalitySchema and InstanceSpecialization and GeneralizationUnit 1 Summary — Introduction to DBMS & ER ModelThree-Level Architecture ANSI/SPARC ArchitectureWeak Entity SetUnit 2 — Relational Model & SQLConstraints in SQLCursorsDCL and TCL CommandsDDL CommandsDML CommandsDomain Relational Calculus DRCFunctions and Stored ProceduresJoins in SQLNested Queries SubqueriesRelational AlgebraRelational CalculusRelational ModelSQL IntroductionUnit 2 Summary — Relational Model & SQLTriggers in SQLTuple Relational Calculus TRCViews in SQLArmstrong's Axioms & Closure of AttributesBoyce-Codd Normal Form BCNFClosure of AttributesDependency PreservationFifth Normal Form 5NFFirst Normal Form 1NFFourth Normal Form 4NFFunctional DependencyLossless DecompositionMultivalued DependencyNormal Forms — OverviewNormalization — IntroductionSecond Normal Form 2NFUnit 3 Summary — NormalizationThird Normal Form 3NFUnit 4 — Transaction Management & Concurrency ControlACID PropertiesCheckpointsConcurrency Control & SerializabilityDeadlock in DBMSLock-Based Protocols & Two-Phase LockingLog-Based RecoveryRecovery SystemSerializabilityShadow PagingUnit 4 Summary — Transaction Management & Concurrency ControlTimestamp-Based ProtocolTransaction ManagementTransaction StatesTwo-Phase Locking 2PLUnit 5 — Storage & IndexingB+ TreeB-TreeCost EstimationDynamic HashingFile OrganizationHashing TechniquesIndexing — IntroductionMulti-Level IndexingQuery OptimizationQuery ProcessingSingle-Level IndexingStatic HashingUnit 5 Summary — Storage & IndexingUnit 6 — Advanced Topics in DBMSBig Data and DBMSCloud DatabaseData MiningData WarehouseDatabase SecurityDistributed DatabaseDistributed Query ProcessingDistributed DBMS Architecture, Fragmentation & ReplicationMongoDB — IntroductionNoSQL DatabaseReplication in Distributed DatabasesUnit 6 Summary — Advanced Topics in DBMSViva Voce — DBMSImportant Viva Questions — DBMSInterview Questions — DBMSViva Answers — DBMSDBMS Multiple Choice Questions MCQsDBMS Lab Programs
Third Normal Form 3NF
Last Updated : 21 May, 2026
A relation is in Third Normal Form 3NF if:
Unit 3141 words7 headingsExamples included
Definition
A relation is in Third Normal Form (3NF) if:
- It is in 2NF, AND
- No non-prime attribute is transitively dependent on the primary key
A transitive dependency occurs when: PK → X → Y (a non-key attribute Y depends on another non-key attribute X, which itself depends on the PK).
Formal Definition
For every non-trivial FD X → A in R, at least one of the following holds:
- X is a superkey of R, OR
- A is a prime attribute (part of some candidate key)
Identifying Transitive Dependencies
| PK | EmpID |
| EmpID | Name, DeptID, ManagerID ← direct ✓ |
| DeptID | DeptName ← DeptName depends on non-key DeptID ✗ |
| ManagerID | ManagerName ← ManagerName depends on non-key ManagerID ✗ |
| EmpID | DeptID → DeptName (transitive via DeptID) |
| EmpID | ManagerID → ManagerName (transitive via ManagerID) |
Decomposition to 3NF
| Step 1 | Find transitive FDs: |
| DeptID | DeptName |
| ManagerID | ManagerName |
| Step 2: For each transitive FD A | B: |
Another Classic Example
| PK | SID |
| FD: SID | Advisor |
| Advisor | AdvisorDept ← transitive via Advisor ✗ |
Visual Diagram
3NF VIOLATION (Transitive Dependency):
┌──────────────────────────────────────────┐
│ Employee(EmpID, DeptID, DeptName) │
│ │
│ EmpID ─────► DeptID ─────► DeptName │
│ (PK) (non-key) (non-key) │
│ ↑ transitive chain ✗ │
└──────────────────────────────────────────┘
AFTER 3NF:
Employee(EmpID, DeptID)
Department(DeptID, DeptName)
✓ No more transitive dependencies
3NF vs BCNF
3NF allows a FD X → A if A is a prime attribute (part of a candidate key), even if X is not a superkey. BCNF does not allow this exception.
| R(A, B, C) with FDs: AB | C, C → A |
| Candidate keys | {AB}, {BC} |
| C | A: C is not a superkey. But A is prime → OK for 3NF ✓ |
| C | A: violates BCNF (C is not a superkey) ✗ |
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Third Normal Form 3NF.
Interview Use
Prepare one clear explanation, one practical example, and one common mistake for this DBMS topic.
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Unit 3Fifth Normal Form 5NFA relation R is in Fifth Normal Form 5NF — also called Project-Join Normal Form PJ/NF — if, for every non-trivial join dependency R1, R2, ..., Rn in R:Unit 3First Normal Form 1NFA relation is in First Normal Form 1NF if:Unit 3Fourth Normal Form 4NFA relation R is in Fourth Normal Form 4NF if, for every non-trivial multivalued dependency X →→ Y in R:Unit 3Second Normal Form 2NFA relation is in Second Normal Form 2NF if:Unit 3Normal Forms — OverviewUnit 3Boyce-Codd Normal Form BCNFA relation R is in BCNF Boyce-Codd Normal Form if, for every non-trivial functional dependency X → Y in R: