Three Level Architecture of DBMS
The generalized architecture of a database system is called ANSI/SPARC model. Many commercial systems and research database models fit within this framework. This architecture is also called Three-Level Architecture of DBMS. The Three-Level Architecture of DBMS is shown below:
It can divided into the following three levels :
1. External or View level
2. Conceptual level
3. Internal or Physical level
External or View level:
The external or view level of the architecture of a Database system is the level closest to the users. This level is concerned with how the data are observed, So, most of the users of the database are not concerned with all the information contained in the database.
It describes that different types of data stored in a database. This level also includes the relationships existing among data items. At this level, a database is also described logically rather than physically in terms of data structure. However, users of this level are not concerned with how these logical data structures will be implemented at the physical level. Rather, they are only concerned about what information would be kept in a database.
The lowest level of abstraction is the internal level. It is the one closest to the physical storage device. So, it is also termed as physical level, because it describes how data are stored on the storage medium such as hard disk, magnetic tape, etc.