3 LEVEL OF DATABASE SYSTEM ARCHITECTURE -:
The major purpose of database system is to provide the user with abstract view of data .that is ,system hides certain thing like how the data is stored and maintained,but on the other hand the data must be retrieve efficiently in order for system is to be useful . Since database end users are not be computer trained ,the complexity hidden from them in order to simplify their interaction with the systems through the three level of Architecture .
The three level of Architecture is known as three schema architecture .The purpose of three level of architecture is to separate the user application and the physical database .The purpose of the separation .,different users needed different view of same data .It can be classified into three level-:
1-view level
2-conceptual and logical level
3-internal and physical level
Internal and physical level -:It is a lowest level of abstraction that describe the how the data are actually stored . Internal level refer to as Physical level .It can be working within a DBMS and operating system .Internal schema written in DDL statement .
Conceptual level- The next higher level of abstraction describe the what data are needed .what are the relationship among the those data .Conceptual level thus describe the entire of the database in the term of small number of relatively simple structure .Although implement of simple structure at the logical level involves complex physical level structure ,the user of the logical level does not need to aware the complexity .it refer to as physical data in-dependency.
view level -:The highest level of abstraction describe only part of the entire database .Even though the logical level uses the simple structure ,complexity remain because the variety of information stored in large database .many user of the database does not need to access all information ,instead of they need to access only part of the database .The system may provide many view of the database..
