What is Three Schema Architecture?
Schema means **structure.
Structure means the way we organize the data we are storing (e.g., Student, Railway).
Example:
Raw Data → 1, A, 20
Same data in a table:
| Roll | Name | Age |
|---|---|---|
| 1 | A | 20 |
Here, Roll number is an integer (int) value.
There are three levels of data abstraction:
1. Conceptual Schema (Designer - Defines How Data is Stored - ER Model)
- Defines the structure of the data.
- Example: What tables and attributes will exist in the student database?
2. Physical Schema (Administrator - Manages Database Storage)
- Defines how and where the data will be stored.
- Example: Database administrators decide how student records are stored in MySQL, Oracle, or another database system.
3. External Schema (User - View Level - Limited Access)
- Users can see and access only limited data but cannot modify or see the full database.
- Example: A student can view their own exam results on the university website but cannot see other students' data.
Types of Database Files:
- Data Files – Store actual data (e.g., student records).
- Log Files – Keep track of changes made to the database.
- Index Files – Speed up searching and retrieving data.
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