Database and DBMS - An Introduction

• Data: Raw, unorganized, unanalyzed facts, numbers, or symbols that lack context and cannot directly guide decision-making.
Example: Rahul, 85, 92, 78 (isolated words and numbers).
• Information: Data that has been processed, organized, and presented in a structured context so that it acquires clear meaning.
Example: "Student Rahul scored 85 in English, 92 in Math, and 78 in Science, securing first division."

• Definition: A Primary Key is a designated field (or combination of fields) in a relational database table that uniquely identifies every individual record in that table.
• Two Essential Rules:
1. Uniqueness: No two records in the table can ever contain identical values in the primary key field.
2. Non-Nullability: The primary key field CANNOT BE NULL (it can never be left empty or blank).

• (a) Field (Attribute / Column): A vertical column in a table that represents a specific property or category of information (e.g., Admission_No, First_Name). All entries in a field share the same data type.
• (b) Record (Tuple / Row): A single horizontal row in a table that contains a complete set of related data about one individual person, item, or transaction.
• (c) Table (Relation): A structured two-dimensional grid of intersecting rows (records) and columns (fields) that stores all data pertaining to a specific entity.

1. Data Redundancy: In paper files, the same customer or student information is duplicated across multiple ledgers, wasting storage space.
   2. Data Inconsistency: Updating an address in one paper file often leaves duplicate records in other files outdated, leading to conflicting records.
   3. Slow Retrieval & Security Risks: Searching through thousands of paper files takes hours, and paper ledgers can be easily damaged by fire, termites, water, or stolen without audit trails.

1. Tables: The foundational storage containers where all raw data is stored in structured columns and rows.
   2. Queries: Specialized questions or instructions executed on the database to search, filter, and extract specific records that satisfy set conditions.
   3. Forms: Interactive graphical screen windows that provide user-friendly interfaces for entering, modifying, and viewing records.
   4. Reports: Formatted and professionally styled print-ready outputs designed to display, summarize, and print database information.

• A student's Name cannot be used as a primary key because names are not guaranteed to be unique. In a large school, multiple students can share the exact same first and last name (e.g., two students named "Rohan Sharma").
• Using "Name" would violate the fundamental uniqueness rule of primary keys and cause catastrophic database record collisions.
• What should be used instead: An Admission Number or Roll Number, which is issued as a strictly unique identifier to every student.

• RDBMS (Relational Database Management System): A database management program based on the Relational Model (developed by Dr. E.F. Codd) in which data is organized into structured, interrelated tables connected by common key fields.
• Two Examples: MySQL, Oracle Database (also Microsoft Access and PostgreSQL).

• The AutoNumber data type automatically generates and assigns a sequential, unique integer number (starting from 1, 2, 3...) to every new record as soon as it is created in the table.
• Because the system guarantees that each generated number is strictly unique and never repeated, AutoNumber fields are commonly selected as the Primary Key for tables.