Components And Overall Structure of DBMS.

Components of DBMS are broadly classified as follows :

1. Query Processor :

(a) DML Compiler
(b) Embedded DML pre-compiler
(c) DDL Interpreter
(d) Query Evaluation Engine

2. Storage Manager :

(a) Authorization and Integrity Manager
(b) Transaction Manager
(c) File Manager
(d) Buffer Manager

3. Data Structure :

(a) Data Files
(b) Data Dictionary
(c) Indices
(d) Statistical Data

1. Query Processor Components :

• DML Pre-compiler : It translates DML statements in a query language into low level instructions that query evaluation engine understands. It also attempts to transform user's request into an equivalent but more efficient form.
• Embedded DML Pre-compiler : It converts DML statements embedded in an application program to normal procedure calls in the host language. The Pre-compiler must interact with the DML compiler to generate the appropriate code.
• DDL Interpreter : It interprets the DDL statements and records them in a set of tables containing meta data or data dictionary.
• Query Evaluation Engine : It executes low-level instructions generated by the DML compiler.

2. Storage Manager Components :

They provide the interface between the low-level data stored in the database and application programs and queries submitted to the system.
• 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 Structures :

Following data structures are required as a part of the physical system implementation.
• Data Files : It stores the database.
• Data Dictionary : It stores meta data (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.