ANSI - SPARC (American National Standards Institute - Standards Planning and Requirements Committee) recognized and approved the three-level architecture for database.
The following is a figure representing the three levels −
It is the Internal Level and is the physical storage of a database
Describes how the data is internally stored. It would also describe the data structures used by the database.
It represents the complete content of the database i.e. the records and relationships. The global view of the database comes in the middle-tier as shown in the below figure.
The conceptual level has the logical structure of the entire database.
External Level as the name suggests, is what the end users view. A database will have one Internal Schema and Conceptual Scheme, whereas it may have more than onE Extrenal Schema formed as per the need of the users.