Structure of DBMS

Structure of DBMS:

DBMS (Database Management System) acts as an interface between the user and the database. The user requests the DBMS to perform various operations (insert, delete, update and retrieval) on the database. The components of DBMS perform these requested operations on the database and provide necessary data to the users. A DBMS is partitioned into modules that deal with each of the responsibilities of the overall system. The functional components of a database system can be broadly divided into the storage manager and the query processor components.

1.      Query Processor:

Query Processor translates statements in a query language into low-level instructions the database manager understands. The Query Processor simplifies and facilitates access to data. The Query processor includes the following component.

· DML Pre-compiler: DML pre-compiler converts DML statements embedded in an application program to normal procedure calls in a host language.  It also attempts to transform user's request into an equivalent query language but more efficient form. The Pre-compiler must interact with the DML compiler to generate the appropriate code.

· DML Compiler: The DML compiler translates DML statements in a query language into an evaluation plan consisting of low-level instructions that the query evaluation engine understands. The DML compiler also performs query optimization, which is it picks the lowest cost evaluation plan from among the alternatives. Query evaluation engine executes low level instructions generated by the DML compiler.

· DDL Interpreter: It interprets the DDL statements and records them in a set of tables containing meta data or data dictionary. It interprets DDL statements and records the definitions in the data dictionary.

·       · Query Evaluation Engine: It executes low-level instructions generated by the DML compiler.

2.      Storage Manager :

Storage Manager provides the interface between the low-level data stored in the database and application programs and queries submitted to the system. The storage manager is responsible for the interaction with the file manager. The raw data are stored on the disk using the file system, which is usually provided by a conventional operating system. The storage manager is responsible for storing, retrieving, and updating data in the database.

· Authorization and Integrity Manager: It tests for the satisfaction of integrity constraints checks the authority of users to access data.

· Transaction Manager: It ensures that the database remains in a consistent state despite the system failures and that concurrent transaction execution proceeds without conflicting.

· File Manager: It manages the allocation of space on disk storage and the data structures used to represent information stored on disk.

· Buffer Manager: It is responsible for fetching data from disk storage into main memory and deciding what data to cache in memory.

3.      Data Structure / Storage :

Following data structures are required as a part of the physical system implementation.

· Data Files: It stores the database.

· Data Dictionary: It stores metadata (data about data) about the structure of the database.

· Indices: Provide fast access to data items that hold particular values.

·Statistical Data: It stores statistical information about the data in the database. This information is used by query processor to select efficient ways to execute query.

-profshardulp.patil@gmail.com