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.
The Three level architecture is shown below:
It can be divided into following three levels :
1. 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 the way in which data are observed by individuals. Most of the users of database are not concerned with all the information contained in the database.
2. Conceptual level : It describes that different types of data actually stored in a database. This level also includes the relationships existing among data items. At this level, a database is described logically rather than physically in terms of data-structure. Users of this level are not concerned with how these logical data structure will be implemented at the physical level. Rather, they are only concerned about what information would be kept in a database.
3. Internal level : The lowest level of abstraction is the internal level. It is the one closest to physical storage device. This level is also termed as physical level, because it describes how data are actually stored on the storage medium such as hard disk, magnetic tape etc.