what are three levels of data abstraction?
There are three levels of abstraction:
- Physical level: The lowest level of abstraction describes how data are stored.
- Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
- View level: The highest level of abstraction describes only part of entire database.
Data abstraction is a process of representing the essential features without
including implementation details.
many database-systems users are not computer trained, developers hide the
complexity from users through several levels of abstraction, to simplify users’
interactions with the system:
1) 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.
2) Logical level.
The next-higher level of abstraction describes what data are
stored in the database, and what relationships exist among those data. The
logical level thus describes the entire database in terms of a small number of
relatively simple structures.
- The major purpose of a database system is to provide users with an abstract view of the system.The system hides certain details of how data is stored and created and maintained
Complexity should be hidden from database users.
- There are several levels of abstraction:
- Physical Level:
- How the data are stored.
- E.g. index, B-tree, hashing.
- Lowest level of abstraction.
- Complex low-level structures described in detail.
- Conceptual Level:
- Next highest level of abstraction.
- Describes what data are stored.
- Describes the relationships among data.
- Database administrator level.
- View Level:
- Highest level.
- Describes part of the database for a particular group of users.
- Can be many different views of a database.
- E.g. tellers in a bank get a view of customer accounts, but not of payroll data.
- Physical Level: