Database Reference
In-Depth Information
The
user level
represents distinct views that are customized to the needs of the individual
users. For example, users in the accounting department would have a view of the database
that included the salaries of employees or fees collection of students while users in the ex-
amination department would have views of academic records of students.
The
logical level
would be a collection of table schemas such as an employee/ student table
and an examination table, each with attributes as columns. This level would include map-
pings to the user schemas.
The
system level
is a collection of software and file schemas. Schema levels make it pos-
sible for users, developers, and database administrators to work within their level without
having to know anything about the other levels.
Let us take an example of college database where we have three tables Student, Course and
Marks Record.
2.3 Database Instance
The term instance is typically used to describe a complete database environment, including
the RDBMS software, table structure, stored procedures and other functionality. It is most
commonly used when administrators describe multiple instances of the same database. It is
the actual data stored in a database at a particular moment in time. It is also called database
state or occurrence.
