Database Levels in DBMS
A Database Management System (DBMS) operates at different levels to manage data efficiently. These levels represent how data is stored, organized, and processed. The three primary levels of database architecture follow the ANSI-SPARC (American National Standards Institute – Standards Planning and Requirements Committee) model, which defines:
- Internal Level (Physical Level)
- Conceptual Level (Logical Level)
- External Level (View Level)
1. Internal Level (Physical Level)
🔹 Definition: The lowest level of the database, responsible for physical storage of data on hardware (disks, SSDs).
🔹 Function:
- Defines how data is stored (file organization, indexing, compression).
- Deals with memory management and access speed.
- Invisible to users and developers, handled by the DBMS.
🔹 Example: Storing data as binary files, B-Trees, or hash indexes on disk.
2. Conceptual Level (Logical Level)
🔹 Definition: The middle level that defines the overall structure of the database.
🔹 Function:
- Specifies tables, relationships, constraints, and data types.
- Ensures data integrity and consistency.
- Hides physical storage details but provides a structured view.
🔹 Example: - A table Employees (id, name, salary, department_id).
- Relationships between Employees and Departments tables.
3. External Level (View Level)
🔹 Definition: The highest level that defines how users interact with data through views and interfaces.
🔹 Function:
- Provides customized views of data for different users.
- Controls access permissions (e.g., a manager sees all salaries, but employees see only their own).
- Simplifies complex data structures for user-friendly access.
🔹 Example: - A Finance Department view that shows only salary-related data.
- A Customer view that hides internal IDs and only displays names and purchases.
Diagram: Database Levels
Comparison Table: Database Levels
| Level | Also Called | Focus | Who Uses It? | Example |
|---|---|---|---|---|
| Internal Level | Physical Level | How data is stored | DBMS, Admins | Files, indexes on disk |
| Conceptual Level | Logical Level | How data is structured | Developers, Designers | Tables, relationships |
| External Level | View Level | How data is accessed | Users, Analysts | Reports, views |
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