A database is an information that is set up for easy access, management and updating. Computer databases typically store aggregations of data records or files that contain information, such as sales transactions, customer data, financials and product information
The three schema architecture divides the database into three-level to create a separation between the physical database and the user application. In simple words, this architecture hides the details of physical storage from the user. The database administrator (DBA) should be able to change the structure of database storage without affecting the user’s view.
This architecture contains three layers or levels of the database management system:
- External level
- Conceptual level
- Internal level
This is the highest level of database abstraction. External or view level describes the actual view of data that is relevant to the particular user. This level also provides different views of the same database for a specific user or a group of users. An external view provides a powerful and flexible security mechanism by hiding the parts of the database from a particular user.
The conceptual level describes the structure of the whole database. This level acts as a middle layer between the physical storage and user view. It explains what data is to be stored in the database, what relationship exists among those data, and what the data types are. There is only one conceptual schema per database.
This is the lowest level of database abstraction. It describes how the data is stored in the database and provides methods to access data from the database. It allows viewing the physical representation of the database on the computer system. The interface between the conceptual schema and the internal schema identifies how an element in the conceptual schema is stored and how it may be accessed.
The three-level architecture is to enable multiple users to access the same data with a personalized view while storing the underlying data only once. Thus it separates the user’s view from the physical structure of the database.