It refers that how database is actually stored in database, what data
and structure of data used by database for data. So describe all this database provides user
with views and these are
Data abstraction.
DBMS hides some information's which is not of user interest, a this
is called data abstraction
So developer hides complexity from user and store abstract view of
data.
Data abstraction has three level of abstractions:
Level / internal level
Logical level / Conceptual level
View level / External level
Instances and schemas.
Design of database is called the Schema.
It is basically skeleton structure that represent the logical view
of entire database.