Levels of Abstraction

There are 3 levels of Abstraction:

• Physical level: describes how data records (e.g., a customer) are stored.

  • This layer is transparent to most of the users. It's visible to Database Administrators.

• Logical level: describes data stored in database, and the relationships among the data.

  type customer = record 
      customer_id : integer;    
      customer_name : string;   
      customer_street : string;   
      customer_city : string; 
  end;
  

• View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes – in this case details are hidden from the application program