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LearnStep 1 of 2
Three-Schema Architecture
Learning Objectives
- •Understand three-schema architecture
- •Learn data independence
Lesson Outline
LearnStep 1/2
Three-Schema Architecture
Schema Levels
| Level | Description | Example |
|---|---|---|
| External | User-specific views | Sales department sees only sales data |
| Conceptual | Community view of data | Tables, relationships, constraints |
| Internal | Physical storage | Files, indexes, storage allocation |
Data Independence
Logical Data Independence
Change conceptual schema without affecting external views:
- Add new table → existing views unchanged
- Add column → views that don't use it unchanged
Physical Data Independence
Change internal schema without affecting conceptual schema:
- Change storage structure
- Add/remove indexes
- Change file organization