What are the different level of data abstraction?

Data abstraction is the technique of hiding the complexity of the database to its users.
There are three levels of data abstraction which are discussed below.
• Physical Level or Internal Level:
It is the lowest level of abstraction and describes how the data in the database are actually
stored. This level describes complex low-level data structures in detail and is concerned
with the way the data is physically stored. Data only exists at physical level.
• Logical Level or Conceptual Level:
This is the next higher level of abstraction and describes what data are stored in the
database, and what relationships exist among those data. It describes the structure of
whole database and hides details of physical storage structure. It concentrates on
describing entities, data types, relationships, attributes and constraints. All of the views
must be derivable from this conceptual schema.
• View Level or External Level:
It is the highest level of abstraction and is concerned with the way the data is seen by
individual users. This level simplifies the users’ interaction with the system. It includes a
number of user views and hence is guided by the end user requirement. It describes only
those part of the database in which the users are interested and hides rest of all from
those users. Each user group refers to its own external schema.
Example:
view level
• View result
• View student information
logical level: entire database schema
• Courses (CourseNo,CourseName,Credits,Dept)
• Student (StudentID,Lname,Fname,Level,Major)
• Grade (StudentID,CourseNo,mark)
physical level:
• how these tables are stored, how many bytes it required etc