- DBMS - Data Independence
- DBMS - Data Schemas
- DBMS - Data Models
- DBMS - Architecture
- DBMS - Overview
- DBMS - Home
Entity Relationship Model
Relational Model
- DBMS- SQL Overview
- DBMS - ER to Relational Model
- DBMS - Relational Algebra
- DBMS - Relational Data Model
Relational Database Design
Storage and File Structure
Indexing and Hashing
Transaction And Concurrency
Backup and Recovery
DBMS Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
DBMS - Data Models
Data models define how the logical structure of a database is modeled. Data Models are fundamental entities to introduce abstraction in a DBMS. Data models define how data is connected to each other and how they are processed and stored inside the system.
The very first data model could be flat data-models, where all the data used are to be kept in the same plane. Earper data models were not so scientific, hence they were prone to introduce lots of duppcation and update anomapes.
Entity-Relationship Model
Entity-Relationship (ER) Model is based on the notion of real-world entities and relationships among them. While formulating real-world scenario into the database model, the ER Model creates entity set, relationship set, general attributes and constraints.
ER Model is best used for the conceptual design of a database.
ER Model is based on −
Entities and their attributes.
Relationships among entities.
These concepts are explained below.
Entity − An entity in an ER Model is a real-world entity having properties called attributes. Every attribute is defined by its set of values called domain. For example, in a school database, a student is considered as an entity. Student has various attributes pke name, age, class, etc.
Relationship − The logical association among entities is called relationship. Relationships are mapped with entities in various ways. Mapping cardinapties define the number of association between two entities.
Mapping cardinapties −
one to one
one to many
many to one
many to many
Relational Model
The most popular data model in DBMS is the Relational Model. It is more scientific a model than others. This model is based on first-order predicate logic and defines a table as an n-ary relation.
The main highpghts of this model are −
Data is stored in tables called relations.
Relations can be normapzed.
In normapzed relations, values saved are atomic values.
Each row in a relation contains a unique value.
Each column in a relation contains values from a same domain.