DBMS Notes
HubUnit 1 — Introduction to DBMS & Entity-Relationship ModelAdvantages and Disadvantages of DBMSAggregation — Database Management SystemsCharacteristics of DBMSData IndependenceData ModelsDatabase Users and AdministratorsDBMS LanguagesER DiagramsEntity-Relationship (ER) ModelIntroduction to DBMSKeys in DBMSRelationships and CardinalitySchema and InstanceSpecialization and GeneralizationDBMS Unit 1 Summary - Database FundamentalsThree-Level Architecture (ANSI/SPARC Architecture)Weak Entity SetUnit 2 — Relational Model & SQLConstraints in SQLCursorsDCL and TCL CommandsDDL CommandsDML CommandsDomain Relational Calculus (DRC) - Complete TutorialFunctions and Stored ProceduresJoins in SQLNested Queries (Subqueries)Relational AlgebraRelational Calculus in Database Management SystemsRelational ModelSQL IntroductionDBMS Unit 2 Summary - SQL and Relational ModelTriggers in SQL — Database Management SystemsTuple Relational Calculus (TRC)Views in SQL — Database Management SystemsArmstrong\Boyce-Codd Normal Form (BCNF) — Database Management SystemsClosure of AttributesDependency PreservationFifth Normal Form (5NF)First Normal Form (1NF) - Database NormalizationFourth Normal Form (4NF)Functional DependencyLossless DecompositionMultivalued DependencyNormal Forms — OverviewNormalization — IntroductionSecond Normal Form (2NF) — Database Management SystemsUnit 3 Summary — NormalizationThird Normal Form (3NF) — Database Management SystemsUnit 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 (2PL)Unit 5 — Storage & IndexingB+ TreeB-TreeCost EstimationDynamic HashingFile OrganizationHashing TechniquesIndexing — IntroductionMulti-Level IndexingQuery Optimization — Database Management SystemsQuery 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 (MCQs)DBMS Lab Programs
The Entity-Relationship (ER) model is a high-level conceptual data model developed by Peter Chen in 1976. It provides a graphical representation of the...
Introduction
The Entity-Relationship (ER) model is a high-level conceptual data model developed by Peter Chen in 1976. It provides a graphical representation of the database structure, making it easy to communicate the design to stakeholders before actual implementation.
The ER model is used during the database design phase and is later translated into a relational schema.
2. Attributes
An attribute is a property or characteristic that describes an entity.
- Represented as an ellipse (oval) connected to the entity by a line
Types of Attributes
| Type | Description | Notation |
|---|---|---|
| Simple | Cannot be subdivided (e.g., Age, Gender) | Regular oval |
| Composite | Can be subdivided (e.g., Name → First, Last) | Connected ovals |
| Single-valued | One value per entity (e.g., StudentID) | Regular oval |
| Multi-valued | Multiple values per entity (e.g., Phone numbers) | Double oval |
| Derived | Computed from other attributes (e.g., Age from DOB) | Dashed oval |
| Key | Uniquely identifies entity instances | Underlined in oval |
| Null | Can have no value (optional attribute) | Regular oval |
3. Relationships
A relationship is an association or connection between two or more entities.
- Represented as a diamond in ER diagrams
- The entities involved are connected to the diamond by lines
Degree of a Relationship
| Degree | Name | Description |
|---|---|---|
| 1 | Unary (Recursive) | Relationship between instances of the same entity |
| 2 | Binary | Relationship between two entities (most common) |
| 3 | Ternary | Relationship involving three entities |
Unary (Recursive)
Ternary
4. Cardinality and Participation
Cardinality specifies the number of instances of one entity that can be associated with instances of another entity through a relationship.
Participation Constraints:
- Total participation (mandatory): Every entity MUST participate — shown as double line
- Partial participation (optional): Some entities may not participate — shown as single line
Entity Sets vs. Relationship Sets
- Entity Set: Collection of entities of the same type (e.g., all students)
- Relationship Set: Collection of relationship instances of the same type (e.g., all enrollments)
Mapping ER to Relational Schema
| ER Concept | Relational Mapping |
|---|---|
| Entity set | Table (relation) |
| Attribute | Column |
| Key attribute | Primary key column |
| Multi-valued attribute | Separate table |
| Composite attribute | Multiple columns or sub-table |
| 1:1 relationship | Foreign key in either table |
| 1:N relationship | Foreign key in the N-side table |
| M:N relationship | New junction (bridge) table |
| Weak entity | Table + foreign key from identifying entity |
Extended ER Features
The Extended ER (EER) model adds:
- Specialization/Generalization — IS-A hierarchies
- Aggregation — Treating a relationship as an entity
- Categories/Union Types — Entity from multiple superclasses
Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Entity-Relationship (ER) Model.
Interview Use
Prepare one clear explanation, one practical example, and one common mistake for this Database Management Systems (DBMS) topic.
Search Terms
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