Three-schema architecture definition
The three-schema architecture is a design approach for databases that splits data views into three layers: what users see, the logical structure, and how data is stored. This separation offers flexibility, data independence, and simpler data management. The method emerged in the 1970s to make handling complex databases easier.
See also: data segregation
Three-schema architecture components
- External schema (user view). This level represents the way individual users or user groups view the data. It shows users specific data views tailored to their needs, hiding unnecessary details.
- Conceptual schema (logical view). This level represents the logical structure of the whole database as seen by the administrator. It combines all user views without showing how data is stored.
- Internal schema (physical view). This level defines how and where the data is stored and accessed.
Benefits of three-schema architecture
- Data independence. When the logical and physical views are separate, changes to one view (especially physical) don't require changes to the other. For instance, changing the storage structure doesn't affect what users see.
- Flexibility. Users can see different views tailored to their needs, making the system more user-friendly and adaptable.
- Efficient data access. The separation allows for tailored optimizations. For example, while a DBA may optimize storage in the internal schema, developers can design efficient queries based on the logical schema.
- Improved security. Providing customized external views to users ensures that they access only the data they are authorized to see.
