database structure

A database structure is divided in different components.  The exact structure of a DBMS is depended upon the operating system on which it has to work because the operating system provide the basic services, which database system uses base for accomplishing it’s tasks.

 

Database structure—-

A database system are divided in two types…

  1. Query processor components
  2. Storage Manager components.

Query processor components-:

Query processor-: This processor accept SQL syntax select a plan for executing the syntax and then executes the chosen file. The User interacts with the query processor and the query processor in turn interacts with the storage engine. The user specified the result and the query processor determine how this result is obtained.

This components are used in evaluating DDL and DML queries and including these components….

  • DML Compiler-: It first attempts to transform user’s request into an equivalent but more efficient from and then translates that into a set of low level instruction that can be used by query evaluation engine.
  • Embedded DML pre-Compiler-: It convert DML statements embedded in an application programme to normal procedure calls in host language. This pre compiler consult DML compiler to generate the appreciate code.
  • DDL Interpreter-: It makes data dictionary which contains metadata.
  • Query evaluation Engine-: It execute low level instruction generated by the DML compiler.

 

Storage Manager components-:

It provide  the interface between the low level data stored in the database and the application programme and queries submitted to the system. These components are ..

  • File Manager-: It manage disk spaces allocation and data structure used to store the data .
  • Buffer Manager-: It is responsible for fetching data from disk to main memory and decides the caching strategy suitable for the application.
  • Transaction Manager-: It ensure consistency of the database after any transaction performed on it.
  • Authorization and Integrity Manager-: It tests for satisfactions of integrity constraints and checks authority of user to access data. It uses all the integrity constraints and authorization rules specified by the DBA.

Data  Structured Used BY DBMS-:

A DBMS  can use several kind of data structured as a part of physical system implement ion.  Each structures has it’s own importance.  some are here ….

  1. Data File – It store the database Itself on the disk.
  2. Data Dictionary -: Information pertaining to the structure and usage of data contained in the database the metadata is maintained in a data dictionary. It is a database itself documents the data. Each database user can consult the data dictionary to learn what each piece of data and various synonyms of the data field mean . In a system where data dictionary is part of DBMS the data dictionary store information concerning the source of each data field value the frequency of its use and audit trial concerning of each data field including the who and when of each update.  Data dictionary stores  …                                                             Names of relations, attributes and each of relation. Domain and lengths,authorised users,accounting information to authorized users,numbers of tuples and indexes etc.
  3. Indices -: This is providing fast access to data items.
  4. Statistical Data-: It store statistical information about the data stored in the database. Like number or records,block etc.

 

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