MySQL + SQL · Lesson 9
Database Architecture and Three-Schema Architecture
Three-Schema Architecture
DBMS uses a three-level (three-schema) architecture to separate the user's view from physical storage. This separation gives data independence.
The Three Levels
| Level | Also Called | Describes |
|---|---|---|
| External | View level | What each user sees (custom views) |
| Conceptual | Logical level | Whole database structure: tables, relationships |
| Internal | Physical level | How data is physically stored on disk |
Main Components of DBMS
- Query processor — understands and runs SQL.
- Storage manager — handles files, indexes and buffers.
- Transaction manager — ensures ACID properties.
- Data dictionary (catalog) — stores metadata.
Summary
- Three levels: external (view), conceptual (logical), internal (physical).
- Components: query processor, storage manager, transaction manager, data dictionary.