MySQL + SQL · Lesson 1
Data Independence
What is Data Independence?
Data independence is the ability to change the schema at one level without changing the schema at the next higher level. It is a major benefit of the three-schema architecture.
Two Types
| Type | Meaning | Example |
|---|---|---|
| Logical data independence | Change conceptual schema without changing external views/apps | Add a new column without breaking existing programs |
| Physical data independence | Change internal storage without changing conceptual schema | Add an index or move to a new disk — queries still work |
Important
Logical data independence is harder to achieve than physical data independence, because application programs depend heavily on the logical structure.
Summary
- Data independence lets you change one schema level without affecting the level above.
- Logical (conceptual changes) and physical (storage changes).
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