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Components of DBMS

Components of DBMS

 

 Different components of DBMS are as follows under:-

  1. Query language: DDL, DML, DCL, TCL (DBMS language)
  2. Query processor or Query language translator
  3. Data manager or Storage manage
  4. Database users

1. Query language:

  • Query language is the computer language which is used to make a query into database.
  • Query is a statement which is used to requesting & retrieval of information from the database
  • Query language is used to retrieve the data & storing the data to the database.

           I. DDL

  • It is known as “Data definition language”
  • It is used to define a database structure or schema.
  • DDL is just like other programming language which get’s input some statements & generates some output
  • Data Dictionary:
    • The output of the DDL is placed at the data dictionary which contains metadata (Data in data).
    • It is considered as an special types of tables.
    • Data dictionary can only accessed & updated by the database system.

 Eg:

Create: Used to create a database & tables or Used to create database object.

Alter: It is used to modify the structure of the database.

Drop: It will be delete the objects from the database

OR

used to delete the database or tables.

      Rename: It is used to rename the database.

 

II.  DML

  • It is known as “Data manipulation language”
  • It is used to manage or manipulate the database tables.
  • Which resolve the “difficulty to access data Problem of the file processing system”
  • Here unlike “File Processing System” we can get the Requested Data Easily Using “Select” Command.
  • There are basically two types of the DML:

            Procedural DML: In procedural user needs to specify that what data are needed & how to get those data.

            Non procedural DML: In this user need to specify only what data are needed, there is no need to specify how to get those data.   

   Eg:

Select: It is used to be retrieving the data from the database.

Insert: It is used to insert the data in to tables.

Update: It is used to update the existing data within a table.

Delete: It is used to delete the records from the table.

 

III.  DCL:

  • It  is known as “Data Control Language”
  • As the name suggest, it is used to control the database.
  • It is used to Assign the access privileges to the users and also used to aw access privileges from the users
  • It Resolve the “Security Problem” of the File Processing System.

Eg:

Grant (To assign the authority): It is used to assign the access privileges to the users.

Revoke: It is used to withdraw access privileges from the users which are given by the grant command.

 

IV. TCL:

  • It  is known as “Transaction Control Language”
  • As the name suggest, it is used to all the transaction of the database.
  • It Resolve the “Atomicity Problem” of the File Processing System.

Eg:

Commit: It is used to save the work done.

Save point (Bookmark): It is used to define a point in database transaction to which you can be later rollback.

Rollback: It is used to restore the database to the particular save point.

 

2. Query language translator or processor

  • As the name suggest, query processor is used to interpret the users query and convert it into efficient series of operations.
  • Finally these operations are sending to data manager for execution.
  • It uses the data dictionary and it selects best path to access data.
    • It includes following components:

1. DDL Interpreters:

  • It interprets DDL statement and records them into the table containing metadata.

2. DML Compilers:

  • It translates the DML statement into low level instructions that the query evaluation engine can understand.

3. Query evaluation engine:

  • It executes the low level instructions generated by the DML compiler.
  • After Compiling All the Low level Data’s are sent to Query evaluation Engine.
  • Query evaluation Engine Evaluate the Low level Instruction and after that it will decide to which Manager to send those low level instruction.

 

3. Storage manager

  • The storage manager is a program model that provides interface between low-level instructions & the application program & query subject to user.
  • It is responsible to interact with the file manager.
  • The storage manger translates the various DML statements into low level file system command.
  • In short, the storage manager is responsible to storing, retrieving & updating data in the database.
  • It includes some of the parts:

1. Data files: It stores the data itself in it.

2. Data dictionary: It stores the metadata about the data structure of the database.

3. Indices: It provides the fast access to data of the database.

It is like “index” of the textbook

 

It includes some important parts:

1. Authorization & Integrity manager:

  • It tests for the satisfaction of integrity constrains and checks the authority of users to access data.

2. Transaction manager:

  • It is responsible to manage all the transaction of the database. It resolves the atomicity problem of the Earlier File processing system.

3. File manager:

  • It is responsible to manage the allocation of space on the disk storage. It will decide at which place to store any of the file.

4. Buffer manager:

  • It is responsible for fetching the data from the disk storage into main memory and deciding what data to catch in the main memory.
  •  It resolves the “difficulty to accessing the data problem” of the file processing system.

 

4. Database users:

  • The users of the database system can be classified in following groups, depending on that degree of the Expertise.

1.      Naive Users:

  • The users who did not be aware of the presence of the database system or any other system supporting their usage are considered as naive users.
  • Naïve users are Normal User who does not aware with Database system.

Like eg:

User of ATM (Automatic teller machine) comes in this category.

 

2.       Application user or Application program:

  • Professional programmer who are responsible for developing application programs are known as application users or application programmers.
  •  The application program could be written in a general purpose programming language such as assembly C,C++,JAVA, COBOL, Pascal etc.

 

3.      Sophisticated users:

  • This users are normally Experienced Users who totally aware with the Database System.
  • This users interact with the system without writing programs instead they form their request in a database query language they submit each query to a query processor, whose function is to break down, DML statements into the instruction that the storage manager understands analysts who submit queries to explore data in the database fall in this category.

4.      Database Administrator (DBA):

  • A person who has such central control over the system is called as a database administrator (DBA).

 

The function of the DBA is as follows under:

 1. Schema definition:

The DBA creates the original database schema by executing a set of data definition statements in the DDL.

2. Storage structure & access method definition:

The DBA also creates appropriate storage structure (table space) & access method by writing set of definitions.

3. Schema & physical organization & modification:
When changing needs of the organization or to improve performance DBA carries out changes the schema or physical organization.

4. Granting light authorization for data access:

By granting different types of authorization the database administrator can regular which are of the database various users can access. The authorization information is kept in a special system structure that the database system consults whenever some attempts to access the data in the system.

5. Routine maintenance:

Example of the DBA routine maintenance activities are:

  • Periodically backing up the database, either on to taps or on to remote services, to prevent loss of data in case of disasters such as flooding.
  • Ensuring that enough free disk space is available for normal operations & upgrading disk space as require.
  • Monitoring jobs on the database& ensuring that performance is not degraded by very expensive task submitted by some users.

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