Three Layer Architecture of Database System

This Database Architecture is called three level architecture because of three layer implementation in this:

1. External Level (also called External Schema or View Level)

2. Conceptual Level (also called Logical Schema or Logical Level)

3. Internal Level (also called Internal Schema or Physical Level)

Three Layer Architecture of DBMS

Let us discuss each layer one by one-

1. External Level (also called External Schema or View Level)

This layer is topmost layer of DBMS system where view of logical level will be shared or displayed. The user or viewer desired result is represented as a view at this layer which is generated by fetching from Database or Logical Level. There are number of viewer can be exist for single conceptual level. The mapping between the View Level and Conceptual Level helps as a channel to get a result in view form from logical level database. This Layer is also called abstraction layer because it only display required view and hide the remaining information from user. The user do not need to know about from where data he gets or what the data structure (or schema) is used to store data. 

2. Conceptual Level (also called Logical Schema or Logical Level)

This Layer is Middle layer of DBMS Architecture where the structure of Database is logically defined. It also ensure the Data Structure used to store the Database, the index definition, Constraint implementation, Security etc. are the role responsibility of this Layer. The DBA (Database Administrator) is responsible for all these responsibilities at this layer.

3. Internal Level (also called Internal Schema or Physical Level)

This Layer is Bottom Layer or Lowest Level of DBMS Architecture that show how the data actually stored in Hard Disk. This Layer is responsible to allocate memory to data and its storage location.