SSC Notes / Computer Awareness / Chapter 9
Chapter 9 of 13

Database Management System (DBMS)

How DBMS organises and manages data, the relational model's key terms, and the basics of SQL commands.

📖 ~13 min read 💻 SSC Computer Awareness

Introduction

A Database Management System (DBMS) is software that stores, organises, and manages data efficiently, allowing users to create, read, update, and delete data without dealing directly with the underlying file structure.

Why DBMS Over Traditional File Systems

Problem with File SystemsHow DBMS Solves It
Data redundancy (same data stored multiple times)Centralised storage minimises duplication
Data inconsistencySingle source of truth keeps data consistent
Difficult concurrent accessDBMS manages multiple users accessing data simultaneously
Weak securityDBMS provides authentication and access-control mechanisms

Relational Database Key Terms

TermMeaning
Table (Relation)A structured set of data organised in rows and columns
Row (Tuple/Record)A single entry in a table
Column (Attribute/Field)A specific category of data in a table
Primary KeyA column (or set of columns) that uniquely identifies each row in a table — cannot be NULL or duplicate
Foreign KeyA column that references the Primary Key of another table, establishing a relationship between tables
Candidate KeyAny column (or set) that could qualify as a Primary Key
📌 Primary vs Foreign Key: A Primary Key uniquely identifies rows WITHIN its own table; a Foreign Key LINKS one table to another by referencing that other table's Primary Key — this relationship is the foundation of the "relational" in relational databases.

Normalization

Normalization is the process of organising database tables to minimise data redundancy and avoid update/insert/delete anomalies, done through a series of "normal forms."

Normal FormKey Rule
1NF (First Normal Form)Each column must hold atomic (indivisible) values — no repeating groups
2NF (Second Normal Form)Must be in 1NF; all non-key attributes fully depend on the entire primary key
3NF (Third Normal Form)Must be in 2NF; no transitive dependency (non-key attributes shouldn't depend on other non-key attributes)

SQL — Structured Query Language

SQL is the standard language used to communicate with relational databases, divided into categories based on function.

CategoryFull FormCommandsPurpose
DDLData Definition LanguageCREATE, ALTER, DROPDefines/modifies database structure (tables, schemas)
DMLData Manipulation LanguageINSERT, UPDATE, DELETEManipulates the actual data within tables
DQLData Query LanguageSELECTRetrieves/queries data
DCLData Control LanguageGRANT, REVOKEControls access permissions
TCLTransaction Control LanguageCOMMIT, ROLLBACKManages database transactions

Popular DBMS Software

DBMSDeveloper/Type
MySQLOpen-source, owned by Oracle
Oracle DatabaseProprietary, Oracle Corporation
MS SQL ServerProprietary, Microsoft
MongoDBOpen-source, NoSQL (non-relational) database
⚠️ SQL vs NoSQL: SQL databases (MySQL, Oracle) are relational, table-based, and use structured schemas. NoSQL databases (MongoDB) are non-relational, more flexible, and better suited for unstructured/rapidly changing data — a modern distinction increasingly tested.
✅ UPSC/SSC Focus: DBMS advantages over file systems · Primary key vs foreign key relationship · Three normal forms (1NF, 2NF, 3NF) basics · SQL command categories (DDL/DML/DQL/DCL/TCL) · SQL vs NoSQL database distinction.

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