Program Data insulation and Data Abstraction

Program Data insulation and Data Abstraction

In traditional file processing,the structure of data files is embedded in the application programs,so the changes to the structure of a file may require changing all programs that access that file.By contrast,DBMS access programs do not require such changes in most cases.The structure of data files is stored in the DBMS catalog separately from the access programs.We call this property as program-data independence.

In some types of database systems,such as object oriented or object relational systems,users can define operations on data as part of the database definitions.An operation is specified into two parts that is the interface(or signature) and the implementation(or method).User application programs can operate on the data by invoking these operations through their names and arguments,regardless of how the operations are implemented.This property is termed as program-operation independence.

A major purpose of a database system is to provide users with an abstract view of the data.That is,a DBMS provides users with a conceptual representation of data that does not include many of the details of how the data is stored or how the operations are implemented.This property is termed as data abstraction.Usually,data abstraction is implemented at three levels:

• Physical level:The lowest level of abstraction,describes how the data are actually stored.The physical level describes complex low-level data structures in detail.
• Logical level:The next higher level of abstraction,describes what data are stored in the database and what relationships exist among those data.The user of the logical level does not need to be aware of this complexity,and is referred as physical data independence or program data independence.  
• View level:The highest level of abstraction,describes only a part of the entire database.The system may provide multiple views for the same database.