The DBMS
accepts the SQL commands generated from a variety of user interfaces, produces
query evaluation plans, executes these plans against the database, and returns
the answers. The major components of DBMS are as follows:
(i) Query processor: The query
processor transforms user queries into a series of low level instructions. It
is used to interpret the online user's query and convert it into an efficient series
of operations in a form capable of being sent to the run time data manager for
execution. The query processor uses the data dictionary to find the structure
of the relevant portion of the database and uses this information in modifying the query and preparing and optimal plan to
access the database.
(ii) Run time database manager: Run time
database manager is the central software component of the DBMS, which
interfaces with user-submitted application programs and queries. It handles
database access at run time. It converts operations in user's queries coming.
Directly via the query processor or indirectly via an application program from
the user's logical view to a physical file system. It accepts queries and
examines the external and conceptual schemas to determine what conceptual
records are required to satisfy the user’s request. It enforces constraints to
maintain the consistency and integrity of the data, as well as its security. It
also performs backing and recovery operations. Run time database manager is
sometimes referred to as the database control system and has the following
components:
• Authorization
control: The authorization control module checks the authorization of
users in terms of various privileges to users.
• Command
processor: The command processor processes the queries passed by
authorization control module.
Integrity
checker: It .checks the
integrity constraints so that only valid data can be entered into the database.
Query
optimizer: The query
optimizers determine an optimal strategy for the query execution.
• Transaction
manager: The transaction manager ensures that the transaction properties should be maintained
by the system.
• Scheduler: It provides an
environment in which multiple users can work on same piece of data at the same
time in other words it supports concurrency.
