Data Models PDF

Data Models =========== Definition: ----------- Organizes data in a database.\ Defines types, relationships, and rules.\ Provides ways to retrieve and update data. Categories: ----------- High-Level (Conceptual): Easy for users to understand.\ Low-Level (Physical): Focuses on storage,...

Data Models =========== Definition: ----------- Organizes data in a database.\ Defines types, relationships, and rules.\ Provides ways to retrieve and update data. Categories: ----------- High-Level (Conceptual): Easy for users to understand.\ Low-Level (Physical): Focuses on storage, for technical experts.\ Representational: Shows data organization, hides storage details. Schemas, Instances, and Database State ====================================== Database Schema: ---------------- Description of database organization.\ Created during design, rarely changes. Schema Diagram: --------------- Visual representation of the schema.\ Shows structure but not actual data. Database State (Snapshot): -------------------------- Data at a specific moment.\ Valid state follows schema rules. Three-Schema Architecture ========================= Levels: ------- Internal Level: Describes physical storage.\ Conceptual Level: Describes database structure for all users.\ External (View) Level: Shows different parts of the database for different users. Goals: ------ Catalog stores database description.\ Separates programs from data.\ Supports multiple user views. Data Independence ================= Logical Data Independence: -------------------------- Difficult to change structure without affecting users/programs. Physical Data Independence: --------------------------- Easier to change storage without affecting users/programs. DBMS Language ============= Data Manipulation Language (DML): --------------------------------- Used to retrieve, add, delete, or update data. Types of DML: ------------- High-Level (Set-Oriented): Works with sets of data.\ Low-Level (Procedural): Works with one record at a time. Database Language: ------------------ SQL combines DDL, VDL, DML, and other features.\ DDL: Defines schemas.\ SDL: Defines internal schema.\ VDL: Defines user views.