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Data Storage and Querying


The database system is divided into two components, i.e 

  • Storage Manager
  • Query Processor

Storage Manager

It is the component of a database system that provides an interface between the low-level data stored, application programs and queries submitted to the system.


The storage manager is in charge of interactions with the file manager. Raw data is stored on the disk using the file system provided by the operating system. It translates various DML statements into Low-level commands. 


  • Authorization and Integrity Manager: Tests for the satisfaction of integrity constraints and checks the authority of users to access data.


  • Transaction Manager: Ensures that the database remains in a uniform state despite system failures where the ongoing transaction executions proceed without conflict.


  • File Manager: Manages the allocation of space on disk storage and therefore the data structures used to represent information on the disk.


  •  Buffer Manager: Accountable for fetching data from disk storage into main memory, and deciding what data to cache in main memory.


  • Data Files: Stores the database itself.


  • Data Dictionary: Stores metadata (data about data) about the structure of the database, specifically, the scheme of the database.


  •  Indices: Provides fast access to data items.


Query Processor

The Query Processor contains 3 components:


  • DDL Interpreter: This interprets the DDL statements and records into the Data Dictionary.


  • DML Compiler: It translates the DML statements into query language consisting of low-level instructions that the query Engine understands.


  • Query Evaluation Engine: Executes low-level instructions generated by the DML compiler


Reference :

Storage and Querying of DBMS.